Resolve warnings about ignored return values

As reported by GCC 10.2 with FORTIFY=1 and SANITIZE=1

src/syncterm/syncterm.c

@@ -1198,7 +1198,8 @@ get_syncterm_filename(char *fn, int fnlen, int type, bool shared)
 	if (!shared) {
 		if (((home == NULL) || (strlen(home) > MAX_PATH - 32))) { /* $HOME just too damn big */
 			if ((type == SYNCTERM_DEFAULT_TRANSFER_PATH) || (type == SYNCTERM_PATH_CACHE)) {
-				getcwd(fn, fnlen);
+				if(getcwd(fn, fnlen) == NULL)
+					return NULL;
 				backslash(fn);
 				if (type == SYNCTERM_PATH_CACHE) {
 					strcat(fn, "cache");
@@ -1539,8 +1540,7 @@ main(int argc, char **argv)
 	    "\tcols#132,lines#60,use=syncterm-bitmap,\n";
 
 	if ((argc == 2) && (strcmp(argv[1], "-T") == 0)) {
-		write(STDOUT_FILENO, syncterm_termcap, strlen(syncterm_termcap));
-		return 0;
+		return write(STDOUT_FILENO, syncterm_termcap, strlen(syncterm_termcap)) > 0 ? EXIT_SUCCESS : EXIT_FAILURE;
 	}
 	if ((argc == 2) && (strcmp(argv[1], "-v") == 0)) {
 		fprintf(stdout, "%s\n", syncterm_version);

src/syncterm/term.c

@@ -62,24 +62,24 @@ static struct ciolib_pixels *pixmap_buffer[2];
 static struct ciolib_mask *mask_buffer;
 static uint8_t pnm_gamma[256] = {
 	0,  13, 22, 28, 34, 38, 42, 46, 50, 53, 56, 59, 61, 64, 66, 69,
-	71, 73, 75, 77, 79, 81, 83, 85, 86, 88, 90, 92, 93, 95, 96, 98, 
-	99, 101, 102, 104, 105, 106, 108, 109, 110, 112, 113, 114, 115, 
-	117, 118, 119, 120, 121, 122, 124, 125, 126, 127, 128, 129, 130, 
-	131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 
-	144, 145, 146, 147, 148, 148, 149, 150, 151, 152, 153, 154, 155, 
-	155, 156, 157, 158, 159, 159, 160, 161, 162, 163, 163, 164, 165, 
-	166, 167, 167, 168, 169, 170, 170, 171, 172, 173, 173, 174, 175, 
-	175, 176, 177, 178, 178, 179, 180, 180, 181, 182, 182, 183, 184, 
-	185, 185, 186, 187, 187, 188, 189, 189, 190, 190, 191, 192, 192, 
-	193, 194, 194, 195, 196, 196, 197, 197, 198, 199, 199, 200, 200, 
-	201, 202, 202, 203, 203, 204, 205, 205, 206, 206, 207, 208, 208, 
-	209, 209, 210, 210, 211, 212, 212, 213, 213, 214, 214, 215, 215, 
-	216, 216, 217, 218, 218, 219, 219, 220, 220, 221, 221, 222, 222, 
-	223, 223, 224, 224, 225, 226, 226, 227, 227, 228, 228, 229, 229, 
-	230, 230, 231, 231, 232, 232, 233, 233, 234, 234, 235, 235, 236, 
-	236, 237, 237, 238, 238, 238, 239, 239, 240, 240, 241, 241, 242, 
-	242, 243, 243, 244, 244, 245, 245, 246, 246, 246, 247, 247, 248, 
-	248, 249, 249, 250, 250, 251, 251, 251, 252, 252, 253, 253, 254, 
+	71, 73, 75, 77, 79, 81, 83, 85, 86, 88, 90, 92, 93, 95, 96, 98,
+	99, 101, 102, 104, 105, 106, 108, 109, 110, 112, 113, 114, 115,
+	117, 118, 119, 120, 121, 122, 124, 125, 126, 127, 128, 129, 130,
+	131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143,
+	144, 145, 146, 147, 148, 148, 149, 150, 151, 152, 153, 154, 155,
+	155, 156, 157, 158, 159, 159, 160, 161, 162, 163, 163, 164, 165,
+	166, 167, 167, 168, 169, 170, 170, 171, 172, 173, 173, 174, 175,
+	175, 176, 177, 178, 178, 179, 180, 180, 181, 182, 182, 183, 184,
+	185, 185, 186, 187, 187, 188, 189, 189, 190, 190, 191, 192, 192,
+	193, 194, 194, 195, 196, 196, 197, 197, 198, 199, 199, 200, 200,
+	201, 202, 202, 203, 203, 204, 205, 205, 206, 206, 207, 208, 208,
+	209, 209, 210, 210, 211, 212, 212, 213, 213, 214, 214, 215, 215,
+	216, 216, 217, 218, 218, 219, 219, 220, 220, 221, 221, 222, 222,
+	223, 223, 224, 224, 225, 226, 226, 227, 227, 228, 228, 229, 229,
+	230, 230, 231, 231, 232, 232, 233, 233, 234, 234, 235, 235, 236,
+	236, 237, 237, 238, 238, 238, 239, 239, 240, 240, 241, 241, 242,
+	242, 243, 243, 244, 244, 245, 245, 246, 246, 246, 247, 247, 248,
+	248, 249, 249, 250, 250, 251, 251, 251, 252, 252, 253, 253, 254,
 	254, 255, 255
 };
 uint8_t pnm_gamma_max = 255;
@@ -2034,7 +2034,8 @@ xmodem_download(struct bbslist *bbs, long mode, char *path)
 
 		if (file_bytes < (ulong)filelength(fileno(fp))) {
 			lprintf(LOG_INFO, "Truncating file to %lu bytes", (ulong)file_bytes);
-			chsize(fileno(fp), (ulong)file_bytes); /* 4GB limit! */
+			if(chsize(fileno(fp), (ulong)file_bytes) != 0) /* 4GB limit! */
+				lprintf(LOG_ERR, "Error %d (%s) truncating file", errno, strerror(errno));
 		}
 		else {
 			file_bytes = filelength(fileno(fp));
@@ -2449,11 +2450,11 @@ buildBt709ToSrgbGamma(const uint8_t maxval) {
     */
 
     uint8_t const linearCutoff709 = (uint8_t) (maxval * 0.018 + 0.5);
-    double const linearCompression709 = 
+    double const linearCompression709 =
         0.018 / (1.099 * pow(0.018, oneOverGamma709) - 0.099);
 
     double const linearCutoffSrgb = 0.0031308;
-    double const linearExpansionSrgb = 
+    double const linearExpansionSrgb =
         (1.055 * pow(0.0031308, oneOverGammaSrgb) - 0.055) / 0.0031308;
 
     int i;