Avoid bogus comparisons when linking fails

This avoids drowning RGBLINK's errors in a meaningless `diff` output

test/asm/test.sh

@@ -114,12 +114,15 @@ for i in *.asm; do
 
 		desired_binname=${i%.asm}.out.bin
 		if [ -f "$desired_binname" ]; then
-			"$RGBLINK" -o "$gb" "$o"
+			if ! "$RGBLINK" -o "$gb" "$o"; then
+				echo "${bold}${red}\`$RGBLINK -o $gb $o\` failed!${rescolors}${resbold}"
+			else
 				rom_size=$(printf %s $(wc -c <"$desired_binname"))
 				dd if="$gb" count=1 bs="$rom_size" >"$output" 2>/dev/null
 				tryCmp "$desired_binname" "$output" gb
 				(( our_rc = our_rc || $? ))
 			fi
+		fi
 
 		(( rc = rc || our_rc ))
 		if [[ $our_rc -ne 0 ]]; then