fix crash caused by decoding all MIME data formats in RichTextHtmlEdit
fix crash caused by decoding all MIME data formats in RichTextHtmlEdit

Under Qt 5.6.0 on Linux, if a program had a large image in its clipboard
that we tried to paste into Mumble's rich text editor, that program would
crash.

The problem code was only enabled in debug mode, so most users would
never have experienced this.

LuAPi/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble,SuperNascher/mumble,Lartza/mumble,LuAPi/mumble,LuAPi/mumble,Lartza/mumble,SuperNascher/mumble,LuAPi/mumble,Lartza/mumble,LuAPi/mumble,SuperNascher/mumble,SuperNascher/mumble,LuAPi/mumble,SuperNascher/mumble,SuperNascher/mumble,Lartza/mumble,SuperNascher/mumble,SuperNascher/mumble,LuAPi/mumble,SuperNascher/mumble,Lartza/mumble,LuAPi/mumble,LuAPi/mumble