COMP: specify default format for vtk::polyWriter constructor (internals)

- gcc-4.8.5 does not respect the default parameter,
  thus specify format explicitly

src/fileFormats/vtk/write/foamVtkPolyWriter.C

@@ -382,7 +382,8 @@ Foam::vtk::polyWriter::polyWriter
     bool parallel
 )
 :
-    polyWriter()
+    // Default parameter fails for gcc-4.8.5, thus specify format here
+    polyWriter(vtk::formatType::INLINE_BASE64)
 {
     open(file, parallel);
 }