"Fix" some completely inane Coverity issues.

None of these were even theoretically possible on any platform, but
I took the opportunity to add bounds checking to bitmap_puttext(),
so that's good I guess.

src/conio/bitmap_con.c

@@ -273,8 +273,6 @@ bitmap_vmem_puttext_locked(int sx, int sy, int ex, int ey, struct vmem_cell *fil
 			|| sy < 1
 			|| ex < 1
 			|| ey < 1
-			|| sx > cio_textinfo.screenwidth
-			|| sy > cio_textinfo.screenheight
 			|| sx > ex
 			|| sy > ey
 			|| ex > cio_textinfo.screenwidth
@@ -882,12 +880,24 @@ static int update_from_vmem(int force)
 /**********************/
 int bitmap_puttext(int sx, int sy, int ex, int ey, void *fill)
 {
-	int x, y;
+	size_t x, y;
 	int ret = 1;
 	uint16_t *buf = fill;
 	struct vstat_vmem *vmem_ptr;
 	struct vmem_cell *vc;
 
+	if (sx < 1
+	    || sy < 1
+	    || ex < 1
+	    || ey < 1
+	    || sx > ex
+	    || sy > ey
+	    || ex > cio_textinfo.screenwidth
+	    || ey > cio_textinfo.screenheight
+	    || fill==NULL) {
+		return(0);
+	}
+
 	pthread_mutex_lock(&vstatlock);
 	vmem_ptr = get_vmem(&vstat);
 	for (y = sy - 1; y < ey; y++) {
@@ -1264,7 +1274,7 @@ void bitmap_clreol(void)
 
 void bitmap_clrscr(void)
 {
-	int x,y;
+	size_t x, y;
 	WORD fill = (cio_textinfo.attribute << 8) | ' ';
 	struct vstat_vmem *vmem_ptr;
 	struct vmem_cell *vc;

src/syncterm/fonts.c

@@ -370,7 +370,7 @@ font_management(void)
 				struct text_info  ti;
 
 				gettextinfo(&ti);
-				savbuf = alloca((ti.screenheight - 2) * ti.screenwidth * sizeof(*savbuf));
+				savbuf = alloca((ti.screenheight - 2U) * ti.screenwidth * sizeof(*savbuf));
 				if (savbuf == NULL) {
 					uifc.helpbuf = "malloc() has failed.  Available Memory is dangerously low.";
 					uifc.msg("malloc() failure.");

src/syncterm/ripper.c

@@ -15084,7 +15084,7 @@ draw_glyph(uint8_t ch)
 			fk = htons(*(uint16_t *)(&fd[off + amiga_font->kernOffset + (ch - amiga_font->first) * 2]));
 		voff = (amiga_font->height - amiga_font->baseline - 1) << doubled;
 		for (i = 0; i < amiga_font->height; i++) {
-			pd = &fd[off + amiga_font->dataOffset + i * amiga_font->modulo];
+			pd = &fd[off + amiga_font->dataOffset + (size_t)i * amiga_font->modulo];
 			pd += (bitoff >> 3);
 			currbit = 7 - (bitoff & 0x07);
 			for (j = 0; j < width; j++) {