BlockInCriticalSectionChecker - silence static analyzer dyn_cast null dereference warning. NFCI.

The static analyzer is warning about a potential null dereference, but we should be able to use cast<> directly and if not assert will fire for us.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@374717 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/StaticAnalyzer/Checkers/BlockInCriticalSectionChecker.cpp b/lib/StaticAnalyzer/Checkers/BlockInCriticalSectionChecker.cpp
index e5b8a6b..0eb3c3d 100644
--- a/lib/StaticAnalyzer/Checkers/BlockInCriticalSectionChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/BlockInCriticalSectionChecker.cpp
@@ -126,7 +126,7 @@
 
 bool BlockInCriticalSectionChecker::isUnlockFunction(const CallEvent &Call) const {
   if (const auto *Dtor = dyn_cast<CXXDestructorCall>(&Call)) {
-    const auto *DRecordDecl = dyn_cast<CXXRecordDecl>(Dtor->getDecl()->getParent());
+    const auto *DRecordDecl = cast<CXXRecordDecl>(Dtor->getDecl()->getParent());
     auto IdentifierInfo = DRecordDecl->getIdentifier();
     if (IdentifierInfo == IILockGuard || IdentifierInfo == IIUniqueLock)
       return true;