gdb/dwarf: add missing bound check to read_loclist_index

gdb/dwarf: add missing bound check to read_loclist_index

read_rnglist_index has a bound check to make sure that we don't go past
the end of the section while reading the offset, but read_loclist_index
doesn't.  Add it to read_loclist_index.

gdb/ChangeLog:

	* dwarf2/read.c (read_loclist_index): Add bound check for the end
	of the offset.

Change-Id: Ic4b55c88860fdc3e007740949c78ec84cdb4da60