Port libgd/libgd/pull/711 (phpGH-16016)

Note that this is not actually security related[1], but still a
reasonable sanity check.

"If a function be advertised to return an error code in the event of
difficulties, thou shalt check for that code, yea, even though the
checks triple the size of thy code and produce aches in thy typing
fingers, for if thou thinkest it cannot happen to me, the gods shall
surely punish thee for thy arrogance." – Henry Spencer

[1] <libgd/libgd#697 (comment)>

Author: cmb69

ext/gd/libgd/gd_tga.c

@@ -191,7 +191,10 @@ int read_header_tga(gdIOCtx *ctx, oTga *tga)
 			return -1;
 		}
 
-		gdGetBuf(tga->ident, tga->identsize, ctx);
+		if (gdGetBuf(tga->ident, tga->identsize, ctx) != tga->identsize) {
+			gd_error("fail to read header ident");
+			return -1;
+		}
 	}
 
 	return 1;