fix(ios): Prevent infinite value in returned location data causing app crash

[dpa99c]

Platforms affected

iOS

Motivation and Context

As outlined in #230, the plugin is sometimes causing app crashes on iOS 14 because one of the values being extracted from the native location object has an infinite value and therefore an exception is raised when trying to extract the values and transform then into a JSON object.

Description

Check the NSMutableDictionary constructed from the native CLLocation data is valid for conversion to JSON using isValidJSONObject before attempting conversion.

Testing

As outlined in #230, I'm not certain exactly which value retrieved from the CLLocation object is INFINITY because the stack trace from the crash only points to the line where the conversion to JSON is attempted but doesn't actually indicate which field in the NSMutableDictionary contains the INFINITE value.

However, the issue can be artificially reproduced by setting one of the values to INFINITY before the conversion is made, e.g. on line 293 of CDVLocation.m:

[returnInfo setObject:[NSNumber numberWithDouble:INFINITY] forKey@"timestamp"];

Without the changes this PR makes, the above will cause an app crash.
With the changes this PR makes, the plugin will return a POSITIONUNAVAILABLE error and the app will not crash.

Checklist

• I've run the tests to see all new and existing tests pass
• [N/A] I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• [N/A] I've updated the documentation if necessary

[breautek]

lgtm