Ok to check in?  This doesn't fix the real problem, which is that
gcj produces vtables that aren't properly abi-compliant.  Hopefully,
we'll fix that.  But for now, let's at least prevent gdb from crashing.

	* gnu-v3-abi.c (gnuv3_rtti_type):  Guard that vtable_symbol_name
	isn't NULL, which can happen with some gcj3.0-produced code.
-- 
	--Per Bothner
per@bothner.com   http://www.bothner.com/per/