CPP: Use strictconcat.

Author: geoffw0

cpp/ql/src/semmle/code/cpp/AutogeneratedFile.qll

@@ -113,7 +113,7 @@ private int fileHeaderLimit(File f) {
 class AutogeneratedFile extends File {
   cached AutogeneratedFile() {
     autogeneratedComment(
-      concat(Comment c |
+      strictconcat(Comment c |
         c.getFile() = this and
         c.getLocation().getStartLine() <= fileHeaderLimit(this) |
         c.getContents() order by c.getLocation().getStartLine()