Show a generic message for unreadable or corrupted trace files.

FileReadError now also signals truncated or malformed traces, not just
mapping failures, so the mmap-specific text misled users.

update/src/update.cpp

@@ -256,7 +256,7 @@ int main( int argc, char** argv )
     }
     catch( const tracy::FileReadError& e )
     {
-        fprintf( stderr, "The file you are trying to open cannot be mapped to memory.\n" );
+        fprintf( stderr, "The file could not be read or is corrupted.\n" );
         exit( 1 );
     }
     catch( const tracy::LegacyVersion& e )