feat(injectedJavaScript): Error replaced by warnings, and callback runs

* Changes error/redbox into warning/yellowbox. So wouldn't crash production releases
* Warning added actual error, useful for debugging bad JS injected into webview
* callback runs, whether there's error or not. As used in my app (https://medium.com/wonderswipe/rethink-mobile-search-10-100x-faster-introducing-wonderswipe-6f2ff0d0e6) which injects JS into sanitized html from the wild, small error in injected JS doesn't warrant the whole JS payload from being injected/run

ios/RNCWKWebView.m

@@ -795,12 +795,11 @@ static NSURLCredential* clientAuthenticationCredential;
           thenCall: (void (^)(NSString*)) callback
 {
   [self.webView evaluateJavaScript: js completionHandler: ^(id result, NSError *error) {
-    if (error == nil) {
-      if (callback != nil) {
-        callback([NSString stringWithFormat:@"%@", result]);
-      }
-    } else {
-      RCTLogError(@"Error evaluating injectedJavaScript: This is possibly due to an unsupported return type. Try adding true to the end of your injectedJavaScript string.");
+    if (callback != nil) {
+      callback([NSString stringWithFormat:@"%@", result]);
+    }
+    if (error != nil) {
+      RCTLogWarn([NSString stringWithFormat:@"Error evaluating injectedJavaScript: This is possibly due to an unsupported return type. Try adding true to the end of your injectedJavaScript string. %@", error]);
     }
   }];
 }