[SIL Printer] Make SILSpecializeAttr printing defensive

Author: DougGregor

lib/SIL/SILPrinter.cpp

@@ -3033,8 +3033,17 @@ void SILSpecializeAttr::print(llvm::raw_ostream &OS) const {
   OS << "exported: " << exported << ", ";
   OS << "kind: " << kind << ", ";
 
-  auto requirements = getSpecializedSignature()->requirementsNotSatisfiedBy(
-      getFunction()->getGenericEnvironment()->getGenericSignature());
+  ArrayRef<Requirement> requirements;
+  SmallVector<Requirement, 4> requirementsScratch;
+  if (auto specializedSig = getSpecializedSignature()) {
+    if (auto env = getFunction()->getGenericEnvironment()) {
+      requirementsScratch = specializedSig->requirementsNotSatisfiedBy(
+          env->getGenericSignature());
+      requirements = requirementsScratch;
+    } else {
+      requirements = specializedSig->getRequirements();
+    }
+  }
   if (!requirements.empty()) {
     OS << "where ";
     SILFunction *F = getFunction();