Warnings For One File Create Emit Warnings For All Files Processed So Far

[lordmilko]

In JavaToCSharpCli, Program.ConvertToCSharpFile attaches an event handler to the JavaConversionOptions.WarningEncountered event handler. However, this event handler is not removed after the ConvertToCSharpFile method finishes converting the file. As a result, when processing multiple files, every file you process will be added to the existing list of delegates attached to this event handler, resulting in all files processed so far receiving warnings that do not apply to them. This change updates ConvertToCSharpFile to ensure the event handler is unregistered prior to the method's return

[paulirwin]

Fixed in #144