Fix heap-use-after-free via setlocale

setlocale returns a statically-allocated memory which can be modified by
subsequent calls of setlocale. This triggers a heap-use-after free in
ASAN when the setlocale function is called again with the previous
pointer.

This was found when trying to use the "Show All Streams" option via
the Telephony -> RTP menu.

While at it, add some modelines

Change-Id: Ide47e877ce828734fd8c5c1b064d9c505ba2b37a
Reviewed-on: https://code.wireshark.org/review/3234
Reviewed-by: Peter Wu <peter@lekensteyn.nl>
Reviewed-by: Evan Huus <eapache@gmail.com>