apk: sanitize return value

Most applets return whatever apk_solver_commit() returns. It is the
number of errors found (or negative for hard error). Sanitize the
error value to not give false success exit code in the unlikely case
of errors % 256 == 0.

Reported-by: Max Justicz <max@justi.cz>

src/apk.c

@@ -689,5 +689,7 @@ int main(int argc, char **argv)
 	apk_string_array_free(&args);
 	free(apk_argv);
 
+	if (r < 0) r = 250;
+	if (r > 99) r = 99;
 	return r;
 }