Hi all,
this patch fixes a problem that I met while debugging a testsuite 
failure on amd64:

 > Running gdb-head/gdb/testsuite/gdb.c++/templates.exp ...
 > FAIL: gdb.c++/templates.exp: constructor breakpoint (timeout)

(gdb) break T5<int>::T5
-> Segfault in linespec.c:486 [decode_line_2()] because
    values.sals[i].symtab is NULL and dereferencing of
    values.sals[i].symtab->filename crashes.

After some investigation I found out that .debug_line section of the 
input file was broken (reported to binutils@ list).
However broken debug info is not an excuse for GDB to crash.

OK to apply to head and branch?

Michal Ludvig
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