Avoid use-after-free in DWARF debug names code

Avoid use-after-free in DWARF debug names code

A static analyzer pointed out that find_vec_in_debug_names will use
the contents of a unique_ptr after it has been destroyed.  This patch
fixes the bug by hoisting the declaration into the appropriate
enclosing block.

I'm checking this in as obvious.

gdb/ChangeLog
2019-07-01  Tom Tromey  <tromey@adacore.com>

	* dwarf2read.c
	(dw2_debug_names_iterator::find_vec_in_debug_names): Hoist
	declaration of without_params.  Fix formatting.