Sema: Fix a fuzzer crash

This test case crashes when prepared overloads are disabled, but passes
when enabled. To avoid messing up tests if we have to turn the flag on
and off, fix the crash.

Author: slavapestov

lib/Sema/ConstraintSystem.cpp

@@ -2924,8 +2924,10 @@ static bool diagnoseContextualFunctionCallGenericAmbiguity(
   // from all the closure contextual fix/solutions and if there are more than
   // one fixed type diagnose it.
   swift::SmallSetVector<Type, 4> genericParamInferredTypes;
-  for (auto &fix : contextualFixes)
-    genericParamInferredTypes.insert(fix.first->getFixedType(resultTypeVar));
+  for (auto &fix : contextualFixes) {
+    if (fix.first->hasFixedType(resultTypeVar))
+      genericParamInferredTypes.insert(fix.first->getFixedType(resultTypeVar));
+  }
 
   if (llvm::all_of(allFixes, [&](FixInContext fix) {
         auto fixLocator = fix.second->getLocator();

validation-test/compiler_crashers/Solution-getFixedType-98b9c4.swift renamed to validation-test/compiler_crashers_fixed/Solution-getFixedType-98b9c4.swift

@@ -1,5 +1,5 @@
 // {"kind":"typecheck","signature":"swift::constraints::Solution::getFixedType(swift::TypeVariableType*) const","signatureAssert":"Assertion failed: (knownBinding != typeBindings.end()), function getFixedType"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 class a {
   static
 b {