Sanity check dwarf5 form of .file

[Alan Modra]

There's a comment a few lines earlier saying that demand_copy_C_string
has already reported an error if it returns NULL.  Given the proximity
I decided not to duplicate the comment.

	* dwarf2dbg.c (dwarf2_directive_filename): Check return of
	demand_copy_C_string for file.

diff --git a/gas/dwarf2dbg.c b/gas/dwarf2dbg.c
index 86dc16108e4..5f2f58ff7b0 100644
--- a/gas/dwarf2dbg.c
+++ b/gas/dwarf2dbg.c
@@ -1195,6 +1195,8 @@ dwarf2_directive_filename (void)
 	{
 	  dirname = filename;
 	  filename = demand_copy_C_string (&filename_len);
+	  if (filename == NULL)
+	    return NULL;
 	  SKIP_WHITESPACE ();
 	}
 

-- 
Alan Modra
Australia Development Lab, IBM