Ignore missing types on for statement expressions

A malformed initializer or increment expression would come out of TypeChecker::typeCheckExpression() with no type, which `checkIgnoredExpr()` was not expecting.

Fixes:

* test/Parse/foreach.swift
* test/Parse/recovery.swift
* test/Parse/toplevel_library_invalid.swift
* test/IDE/complete_stmt_controlling_expr.swift
* validation-test/compiler_crashers_fixed/01736-void.swift
* validation-test/compiler_crashers_fixed/00587-swift-pattern-foreachvariable.swift

Author: beccadax

lib/Sema/TypeCheckStmt.cpp

@@ -1069,6 +1069,12 @@ void TypeChecker::checkIgnoredExpr(Expr *E) {
     }
     return;
   }
+  
+  // Skip checking if there is no type, which presumably means there was a 
+  // type error.
+  if (!E->getType()) {
+    return;
+  }
 
   // Complain about l-values that are neither loaded nor stored.
   if (E->getType()->isLValueType()) {