debugedit: edit_dwarf2 check lndx is in range before checking r_offset.

upstream commit 7e9af0c000868ad6272a9577f9daed991599419b
--- ./tools/debugedit.c.orig	2017-12-05 11:59:10.287010024 +0000
+++ ./tools/debugedit.c	2017-12-05 12:00:02.776862694 +0000
@@ -2171,10 +2171,10 @@ edit_dwarf2 (DSO *dso)
 			  r_offset = rel.r_offset;
 			}
 
-		      while (r_offset > (dso->lines.table[lndx].old_idx
-					 + 4
-					 + dso->lines.table[lndx].unit_length)
-			     && lndx < dso->lines.used)
+		      while (lndx < dso->lines.used
+			     && r_offset > (dso->lines.table[lndx].old_idx
+					    + 4
+					    + dso->lines.table[lndx].unit_length))
 			lndx++;
 
 		      if (lndx >= dso->lines.used)