fix: ios - untracable crashes when URL is not parsable (#183)

Due to NSURL checking compliance with RFC 2396 while parsing the url, sometimes when the URL is not compilant with the RFC it is considered `nil` and code throws this error. The problem is that this error is not caught anywhere, therefore crashing with a very unhelpful stack trace, as seen here: Vydia/react-native-background-upload#121

ios/VydiaRNFileUploader.m

@@ -156,9 +156,9 @@ - (void)copyAssetToFile: (NSString *)assetUrl completionHandler: (void(^)(NSStri
     @try {
         NSURL *requestUrl = [NSURL URLWithString: uploadUrl];
         if (requestUrl == nil) {
-            @throw @"Request cannot be nil";
+            return reject(@"RN Uploader", @"URL not compliant with RFC 2396", nil);
         }
-
+      
         NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:requestUrl];
         [request setHTTPMethod: method];