Prevent loop in parseAddress: if the address is invalid and looks like:

Thijs <aap
(no closing ">"), parseAddress would enter an infinite loop. This is
solved by increasing $pos when no closing > is found. Closes 742584,
thanks Jeroen van Wolffelaar.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@4939 7612ce4b-ef26-0410-bec9-ea0150e637f0