CIndex: Don't crash when visitor passes null child statements, and sprinkle some
asserts in cursor construction functions to make this more obvious.

Doug, please check. c-index-test would previously crash on this code:
--
for(;;) {}
--
Do we need a custom visit of the for statement to cover the variable
declarations?

llvm-svn: 94391
diff --git a/clang/tools/CIndex/CIndex.cpp b/clang/tools/CIndex/CIndex.cpp
index 84f908d..4436709 100644
--- a/clang/tools/CIndex/CIndex.cpp
+++ b/clang/tools/CIndex/CIndex.cpp
@@ -783,7 +783,7 @@
 bool CursorVisitor::VisitStmt(Stmt *S) {
   for (Stmt::child_iterator Child = S->child_begin(), ChildEnd = S->child_end();
        Child != ChildEnd; ++Child) {
-    if (Visit(MakeCXCursor(*Child, StmtParent, TU)))
+    if (*Child && Visit(MakeCXCursor(*Child, StmtParent, TU)))
       return true;
   }