added a chk_non_negative check

cgit.h

@@ -157,6 +157,7 @@ extern void cgit_querystring_cb(const char *name, const char *value);
 
 extern int chk_zero(int result, char *msg);
 extern int chk_positive(int result, char *msg);
+extern int chk_non_negative(int result, char *msg);
 
 extern int hextoint(char c);
 extern char *trim_end(const char *str, char c);

shared.c

@@ -86,6 +86,13 @@ int chk_positive(int result, char *msg)
 	return result;
 }
 
+int chk_non_negative(int result, char *msg)
+{
+    	if (result < 0)
+	    	die("%s: %s",msg, strerror(errno));
+	return result;
+}
+
 struct repoinfo *add_repo(const char *url)
 {
 	struct repoinfo *ret;