Fix undefined comparison of pointer to string literal

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@39014 15284696-431f-4ddb-bdfa-cd5b030d7da7

gem/tools.c

@@ -53,7 +53,7 @@ char *basename(char *path)
 	if ((backup != NULL) && (element != NULL)) {
 	    free(backup);
 	}
-	if ((element != NULL) && (element != "")) {
+	if ((element != NULL) && (*element != '\0')) {
 	    backup = strdup(element);
 	}
     }