[lld-macho] Fix crash on invalid framework tbd

[keith]

Summary

Previously these would crash because file is null in the case there is
an invalid tbd file.

[thakis]

Thanks! :)

lld/MachO/Driver.cpp

if (auto *dylibFile = dyn_cast_or_null<DylibFile>(file)) {
       if (isNeeded)
         dylibFile->forceNeeded = true;
       if (isWeak)
         dylibFile->forceWeakImport = true;
       if (isReexport) {
         config->hasReexports = true;
         dylibFile->reexport = true;
       }
-    } else if (isa<ObjFile>(file) || isa<BitcodeFile>(file)) {
+    } else if (isa_and_nonnull<ObjFile>(file) ||
+               isa_and_nonnull<BitcodeFile>(file)) {
       // Cache frameworks containing object or bitcode files to avoid duplicate
       // symbols. Frameworks containing static archives are cached separately
       // in addFile() to share caching with libraries, and frameworks
       // containing dylibs should allow overwriting of attributes such as
       // forceNeeded by subsequent loads
       loadedObjectFrameworks.insert(*path);
     }
     return;

lld/test/MachO/invalid/invalid-stub.s

 # REQUIRES: x86
-# RUN: mkdir -p %t
+# RUN: mkdir -p %t/invalidYAML.framework
 # RUN: echo "--- !tapi-tbd-v3" > %t/libinvalidYAML.tbd
 # RUN: echo "invalid YAML" >> %t/libinvalidYAML.tbd
+# RUN: cp %t/libinvalidYAML.tbd %t/invalidYAML.framework/invalidYAML.tbd
 # RUN: llvm-mc -filetype obj -triple x86_64-apple-darwin %s -o %t/test.o
 # RUN: not %lld -L%t -linvalidYAML %t/test.o -o %t/test 2>&1 | FileCheck %s -DDIR=%t
+# RUN: not %lld -F%t -framework invalidYAML %t/test.o -o %t/test 2>&1 | FileCheck %s -DDIR=%t --check-prefix=CHECK-FRAMEWORK
 
 # CHECK: could not load TAPI file at [[DIR]]{{[\\/]}}libinvalidYAML.tbd: malformed file
+# CHECK-FRAMEWORK: could not load TAPI file at [[DIR]]{{[\\/]}}invalidYAML.framework{{[\\/]}}invalidYAML.tbd: malformed file
 
 .globl _main
 _main:
   ret