makeCompareUrl() to handle sources with no url

Author: djonas-noip

README.md

@@ -101,4 +101,5 @@ Thanks to everyone who has shared ideas and code! In particular,
 - https://github.com/paxal
 - https://github.com/nclavaud
 - https://github.com/cafferata
+- https://github.com/ihor-sviziev
 

composer-lock-diff

@@ -182,7 +182,7 @@ function mustDecodeJson($json, $context) {
 }
 
 function makeCompareUrl($pkg, $diff) {
-    $func = 'formatCompare' . ucfirst(getSourceRepoType($pkg->source->url));
+    $func = 'formatCompare' . ucfirst(getSourceRepoType((string) @$pkg->source->url));
     return call_user_func($func, $pkg->source->url, $diff[$pkg->name][0], $diff[$pkg->name][1]);
 }