SDK crashed in case of network error

[endrelovas]

All kind of endpoint queries have one basic bug within BAAClient.m
getPath, postPath, putPath, deletePath tries to convert empty (nil) response to NSDictionary which causes the SDK to crash immediately.

This part:

    [[self.session dataTaskWithRequest:request
                     completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {

                         NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
                         NSDictionary *jsonObject = [NSJSONSerialization JSONObjectWithData:data
                                                                                    options:kNilOptions
                                                                                      error:nil];

It should investigate the error return with the completionHandler prior to convert JSON to NSDictionary.
Something like this (not a full code, never tested)

    [[self.session dataTaskWithRequest:request
                     completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
                         if (error) {
                             failure(error);
                             return;
                         }

                         NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
                         NSDictionary *jsonObject = [NSJSONSerialization JSONObjectWithData:data
                                                                                    options:kNilOptions
                                                                                      error:nil];

[xinufje]

Pull request #45 fixes this.