fix VirtualFile::read_file() for text files

panda/src/express/virtualFileMount.cxx

@@ -74,7 +74,7 @@ read_file(const Filename &file, bool do_uncompress,
   }
 
   off_t file_size = get_file_size(file, in);
-  if (file_size != 0) {
+  if (file_size > 0) {
     result.reserve((size_t)file_size);
   }
 

panda/src/express/virtualFileMountSystem.cxx

@@ -127,17 +127,25 @@ open_read_file(const Filename &file) const {
 //               the size.
 ////////////////////////////////////////////////////////////////////
 off_t VirtualFileMountSystem::
-get_file_size(const Filename &, istream *stream) const {
+get_file_size(const Filename &file, istream *stream) const {
   // First, save the original stream position.
   streampos orig = stream->tellg();
 
   // Seek to the end and get the stream position there.
   stream->seekg(0, ios::end);
+  if (stream->fail()) {
+    // Seeking not supported.
+    stream->clear();
+    return get_file_size(file);
+  }
   streampos size = stream->tellg();
 
   // Then return to the original point.
   stream->seekg(orig, ios::beg);
 
+  // Make sure there are no error flags set as a result of the seek.
+  stream->clear();
+
   return size;
 }