qdl: Fail fast when programmer is unavailable

Having the tool fail due to missing images before we establish the USB
connection turns out to be rather nice, so let's do the same thing with
the flash programmer.

Signed-off-by: Bjorn Andersson <[email protected]>

Author: quic-bjorande

qdl.c

@@ -238,6 +238,8 @@ int main(int argc, char **argv)
 		print_version();
 
 	prog_mbn = argv[optind++];
+	if (access(prog_mbn, F_OK))
+		errx(1, "unable to load programmer \"%s\"", prog_mbn);
 
 	do {
 		type = detect_type(argv[optind]);