strace-log-merge: fix file suffix calculation

* strace-log-merge: Quote file prefix to fix file suffix calculation.

Reported-by: Denys Vlasenko <vda.linux@googlemail.com>
Suggested-by: Andreas Schwab <schwab@linux-m68k.org>
diff --git a/strace-log-merge b/strace-log-merge
index 14b3bf1..8ab2409 100755
--- a/strace-log-merge
+++ b/strace-log-merge
@@ -25,7 +25,7 @@
 
 for file in "$logfile".*; do
 	[ -f "$file" ] || continue
-	suffix=${file#$logfile.}
+	suffix=${file#"$logfile".}
 	[ "$suffix" -gt 0 ] 2> /dev/null ||
 		continue
 	pid=$(printf "%-5s" $suffix)