Fixes a few casts in the DisassemblyDialog and PluginSelectorPanel.

We are casting wxWidget's events userdata from void* to integers.
So use uptr instead since it'll work on both x86_32 and x86_64.
Merge pull request #175 from Sonicadvance1/x86_64-dialog-casts

Fixes a few casts in the DisassemblyDialog and PluginSelectorPanel.