Unsafe pointer access in UDP Callback

[guilyx]

Description

m_msg_creator variable was initialized after UDP callback function was established so whenever a UDP packet came, if it so happened that m_msg_creator was not initialized yet, it would crash because the callback function accesses m_msg_creator

Fix

• Added a check in UDP callback function for m_msg_creator object is not null.
• Moved the m_msg_creator initialization statement from on_activate() to just after UDP callback initialization in on_configure().

Results

Removes the often occurring segmentation faults on start up

[lenpuc]

Tested and merged.

Thanks for finding this fix