[PDB][NativeSession] Use better error code for invalid format

Replaces the default "Success" std::error_code with a more meaningful one.

Author: MuellerMP

llvm/lib/DebugInfo/PDB/Native/NativeSession.cpp

@@ -99,9 +99,12 @@ loadPdbFile(StringRef PdbPath, std::unique_ptr<BumpPtrAllocator> &Allocator) {
   PdbPath = Buffer->getBufferIdentifier();
   file_magic Magic;
   auto EC = identify_magic(PdbPath, Magic);
-  if (EC || Magic != file_magic::pdb)
+  if (EC)
     return make_error<RawError>(EC);
 
+  if (Magic != file_magic::pdb)
+    return make_error<RawError>(raw_error_code::invalid_format);
+
   auto Stream = std::make_unique<MemoryBufferByteStream>(
       std::move(Buffer), llvm::endianness::little);
 
@@ -154,9 +157,12 @@ Error NativeSession::createFromExe(StringRef ExePath,
 
   file_magic Magic;
   auto EC = identify_magic(PdbPath.get(), Magic);
-  if (EC || Magic != file_magic::pdb)
+  if (EC)
     return make_error<RawError>(EC);
 
+  if (Magic != file_magic::pdb)
+    return make_error<RawError>(raw_error_code::invalid_format);
+
   auto Allocator = std::make_unique<BumpPtrAllocator>();
   auto File = loadPdbFile(PdbPath.get(), Allocator);
   if (!File)