[CSGen] Fail early if pattern binding is incorrect

It's possible for `TypeChecker::typeCheckPattern` to produce
either no type or type containing error. That should be detected
early and immediately fail constraint generation.

Author: xedin

lib/Sema/CSGen.cpp

@@ -3930,6 +3930,10 @@ bool ConstraintSystem::generateConstraints(
       auto contextualPattern = ContextualPattern::forRawPattern(pattern, dc);
       Type patternType = TypeChecker::typeCheckPattern(contextualPattern);
 
+      // Fail early if pattern couldn't be type-checked.
+      if (!patternType || patternType->hasError())
+        return true;
+
       auto init = patternBinding->getInit(index);
       if (!init) {
         llvm_unreachable("Unsupported pattern binding entry");