Add conditional check for PDB location

File.OpenRead can throw if pdb.PdbLocation is a directory.

This can happen if (for some reason) the pdb file is not found.
In which case PdbLocation will return the working directory, causing
File.OpenRead to throw.

src/BinaryParsers/PEBinary/PortableExecutable/PE.cs

@@ -868,7 +868,11 @@ private bool TryGetPortablePdbMetadataReader(Pdb pdb, out MetadataReader pdbMeta
                 out MetadataReaderProvider pdbProvider,
                 out _))
             {
-                pdbProvider = MetadataReaderProvider.FromPortablePdbStream(File.OpenRead(pdb.PdbLocation));
+                if (File.Exists(pdb.PdbLocation))
+                {
+                    pdbProvider = MetadataReaderProvider.FromPortablePdbStream(File.OpenRead(pdb.PdbLocation));
+                }
+
                 if (pdbProvider == null)
                 {
                     pdbMetadataReader = null;