examples/network/git2.c: exit with proper status, and avoid segfault

This function should exit after printing usage information if too few
arguments were specified.

Additionally, it should exit with a failure status if the first argument
supplied is not one in the internal command list.

examples/network/git2.c

@@ -45,6 +45,7 @@ int main(int argc, char **argv)
 
 	if (argc < 2) {
 		fprintf(stderr, "usage: %s <cmd> [repo]\n", argv[0]);
+		exit(EXIT_FAILURE);
 	}
 
 	for (i = 0; commands[i].name != NULL; ++i) {
@@ -53,5 +54,5 @@ int main(int argc, char **argv)
 	}
 
 	fprintf(stderr, "Command not found: %s\n", argv[1]);
-  
+	return 1;
 }