Fix install referrer order of compare

Author: nonelse

Adjust/adjust/src/main/java/com/adjust/sdk/ActivityHandler.java

@@ -1296,9 +1296,13 @@ private void sendInstallReferrerI(final long clickTime, final long installBegin,
             return;
         }
 
-        if (activityState.clickTime == clickTime
-                && activityState.installBegin == installBegin
-                && activityState.installReferrer.equals(installReferrer)) {
+        if (installReferrer == null) {
+            return;
+        }
+
+        if (clickTime == activityState.clickTime
+                && installBegin == activityState.installBegin
+                && installReferrer == activityState.installReferrer) {
             // Same click already sent before, nothing to be done.
             return;
         }