[syntax parser] Fix another assertion hit related to invalid composition type

Found by the stress tester.

Author: akyrtzi

lib/Parse/ParseType.cpp

@@ -729,11 +729,12 @@ Parser::parseTypeSimpleOrComposition(Diag<> MessageID,
     addType(ty.getPtrOrNull());
   } while (Tok.isContextualPunctuator("&"));
 
-  if (SyntaxContext->isEnabled() && Status.isSuccess()) {
-    auto LastNode = ParsedSyntaxRecorder::makeCompositionTypeElement(
-        SyntaxContext->popIf<ParsedTypeSyntax>().getValue(), None,
-        *SyntaxContext);
-    SyntaxContext->addSyntax(LastNode);
+  if (SyntaxContext->isEnabled()) {
+    if (auto synType = SyntaxContext->popIf<ParsedTypeSyntax>()) {
+      auto LastNode = ParsedSyntaxRecorder::makeCompositionTypeElement(
+          synType.getValue(), None, *SyntaxContext);
+      SyntaxContext->addSyntax(LastNode);
+    }
   }
   SyntaxContext->collectNodesInPlace(SyntaxKind::CompositionTypeElementList);
 

test/Syntax/Parser/fixed_crashers.swift

@@ -2,4 +2,7 @@
 // RUN: %swift-syntax-parser-test %s -dump-tree | %FileCheck %s
 
 let x: a[i] & b
-// CHECK: |let|
+// CHECK: |x|
+
+let x2: a & b[1]
+// CHECK: |x2|