Fix more Coverity "Issues"

Add some malloc() return checks, comment fall-throughs, and resolve
a sleep while holding lock.

None of these should actually matter, so hopefully I didn't add a
new bug.

src/conio/cterm.c

@@ -1270,6 +1270,7 @@ clear2bol(struct cterminal * cterm)
 
 	CURR_XY(&x, &y);
 	buf = malloc(x * sizeof(*buf));
+	if (buf) {
 		for(i = 0; i < x; i++) {
 			if (i > 0)
 				buf[i] = buf[0];
@@ -1286,6 +1287,10 @@ clear2bol(struct cterminal * cterm)
 		vmem_puttext(minx, y, x, y, buf);
 		free(buf);
 	}
+	else {
+		fprintf(stderr, "malloc() in clear2bol()\n");
+	}
+}
 
 void
 cterm_clearscreen(struct cterminal *cterm, char attr)
@@ -1682,15 +1687,38 @@ static void parse_sixel_string(struct cterminal *cterm, bool finish)
 				return;
 			if (cterm->sx_pixels == NULL) {
 				cterm->sx_pixels = malloc(sizeof(struct ciolib_pixels));
+				if (cterm->sx_pixels != NULL) {
 					cterm->sx_pixels->pixels = malloc(sizeof(cterm->sx_pixels->pixels[0]) * cterm->sx_iv * ti.screenwidth * vparams[vmode].charwidth * 6);
+					if (cterm->sx_pixels->pixels != NULL) {
 						cterm->sx_pixels->pixelsb = NULL;
 						cterm->sx_pixels->width = ti.screenwidth * vparams[vmode].charwidth;
 						cterm->sx_pixels->height = cterm->sx_iv * 6;
 						cterm->sx_mask = malloc(sizeof(struct ciolib_mask));
+						if (cterm->sx_mask != NULL) {
 							cterm->sx_mask->width = cterm->sx_pixels->width;
 							cterm->sx_mask->height = cterm->sx_pixels->height;
 							cterm->sx_mask->bits = malloc((cterm->sx_iv * 6 * ti.screenwidth * vparams[vmode].charwidth * 6 + 7)/8);
+							if (cterm->sx_mask->bits != NULL)
 								memset(cterm->sx_mask->bits, 0, (cterm->sx_iv * 6 * ti.screenwidth * vparams[vmode].charwidth * 6 + 7)/8);
+							else {
+								FREE_AND_NULL(cterm->sx_mask);
+								free(cterm->sx_pixels->pixels);
+								FREE_AND_NULL(cterm->sx_pixels);
+							}
+						}
+						else {
+							free(cterm->sx_pixels->pixels);
+							FREE_AND_NULL(cterm->sx_pixels);
+						}
+					}
+					else {
+						FREE_AND_NULL(cterm->sx_pixels);
+					}
+				}
+			}
+			if (cterm->sx_pixels == NULL) {
+				fprintf(stderr, "Error allocating memory for sixel data\n");
+				return;
 			}
 			if (cterm->sx_x == cterm->sx_left && cterm->sx_height && cterm->sx_width && cterm->sx_first_pass) {
 				/* Fill in the background of the line */
@@ -1879,6 +1907,9 @@ all_done:
 			setpixels(cterm->sx_x, cterm->sx_y, cterm->sx_x + cterm->sx_width - 1, cterm->sx_y + cterm->sx_height - 1, 0, 0, 0, 0, &px, NULL);
 			free(px.pixels);
 		}
+		else {
+			fprintf(stderr, "Error allocating memory for sixel data\n");
+		}
 	}
 
 	if (cterm->extattr & CTERM_EXTATTR_SXSCROLL) {

src/conio/sdl_con.c

@@ -708,11 +708,14 @@ static void sdl_add_key(unsigned int keyval, struct video_stats *vs)
 			return;
 		}
 		if((sdl_keynext+2==sdl_key) && keyval > 0xff) {
-			if(keyval==CIO_KEY_MOUSE)
+			if(keyval==CIO_KEY_MOUSE) {
 				sdl_pending_mousekeys+=2;
-			else
-				beep();
 				pthread_mutex_unlock(&sdl_keylock);
+			}
+			else {
+				pthread_mutex_unlock(&sdl_keylock);
+				beep();
+			}
 			return;
 		}
 		sdl_keybuf[sdl_keynext++]=keyval & 0xff;

src/conio/x_events.c

@@ -1264,7 +1264,7 @@ local_draw_rect(struct rectlist *rect)
 {
 	int x, y, xoff = 0, yoff = 0;
 	unsigned int r, g, b;
-	unsigned long pixel;
+	unsigned long pixel = 0;
 	int cleft;
 	int cright = -100;
 	int ctop;