Custom matchers fail to behave as expected

If they return false, that should be respected.

Submitted via @tjgrathwell

[Finish #58184156]
close #434

lib/jasmine-core/jasmine.js

@@ -1781,9 +1781,9 @@ getJasmineRequireObj().matchersUtil = function(j$) {
     var result = true;
 
     for (var i = 0; i < customTesters.length; i++) {
-      result = customTesters[i](a, b);
-      if (result) {
-        return true;
+      var customTesterResult = customTesters[i](a, b);
+      if (!j$.util.isUndefined(customTesterResult)) {
+        return customTesterResult;
       }
     }