[Parse] Set ErrorType to invalid ParamDecl

TypeChecker assumes invalid decl has valid type.

https://bugs.swift.org/browse/SR-8475
rdar://problem/43057057

lib/Parse/ParsePattern.cpp

@@ -431,6 +431,14 @@ mapParsedParameters(Parser &parser,
                                      paramNameLoc, paramName, Type(),
                                      parser.CurDeclContext);
     param->getAttrs() = paramInfo.Attrs;
+
+    auto setInvalid = [&]{
+      if (param->isInvalid())
+        return;
+      param->getTypeLoc().setInvalidType(ctx);
+      param->setInvalid();
+    };
+
     bool parsingEnumElt
       = (paramContext == Parser::ParameterContextKind::EnumElement);
     // If we're not parsing an enum case, lack of a SourceLoc for both
@@ -440,7 +448,7 @@ mapParsedParameters(Parser &parser,
     
     // If we diagnosed this parameter as a parse error, propagate to the decl.
     if (paramInfo.isInvalid)
-      param->setInvalid();
+      setInvalid();
     
     // If a type was provided, create the type for the parameter.
     if (auto type = paramInfo.Type) {
@@ -464,8 +472,7 @@ mapParsedParameters(Parser &parser,
       if (!param->isInvalid())
         parser.diagnose(param->getLoc(), diag::missing_parameter_type);
       
-      param->getTypeLoc() = TypeLoc::withoutLoc(ErrorType::get(ctx));
-      param->setInvalid();
+      setInvalid();
     } else if (paramInfo.SpecifierLoc.isValid()) {
       StringRef specifier;
       switch (paramInfo.SpecifierKind) {