Fix: Dial Prompt / Overlap Dialing Issue (Reported/Tested by Dan Huynh (normal mode), Patched/Tested by Pavel Troller (immediate mode))

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5628 43c1dc8c-776e-4df2-8ef1-6e829299be21