filetop still shows no writes

Similar to: https://github.com/iovisor/bcc/issues/1667

Just tried the command in Android x86 emulator running 4.14 kernel:
```
while true; do cat testfile > /dev/null; echo "asdfasdf" >> testfile; done
```

And I still see the issue. First issue is wrong filename is displayed (I was expecting to see `testfile`) second issue is write column is 0. This is using latest BCC
```
TID COMM READS WRITES R_Kb W_Kb T FILE
2463 clear 2 0 60 0 R screen-256color
2296 cat 35 0 35 0 R ld.config.Q.txt
2363 cat 35 0 35 0 R ld.config.Q.txt
2357 cat 35 0 35 0 R ld.config.Q.txt
2170 cat 35 0 35 0 R ld.config.Q.txt
2373 cat 35 0 35 0 R ld.config.Q.txt
2280 cat 35 0 35 0 R ld.config.Q.txt
2299 cat 35 0 35 0 R ld.config.Q.txt
2443 cat 35 0 35 0 R ld.config.Q.txt
2347 cat 35 0 35 0 R ld.config.Q.txt
2381 cat 35 0 35 0 R ld.config.Q.txt
2257 cat 35 0 35 0 R ld.config.Q.txt
2469 cat 35 0 35 0 R ld.config.Q.txt
2288 cat 35 0 35 0 R ld.config.Q.txt
2175 cat 35 0 35 0 R ld.config.Q.txt
2440 cat 35 0 35 0 R ld.config.Q.txt
2256 cat 35 0 35 0 R ld.config.Q.txt
2374 cat 35 0 35 0 R ld.config.Q.txt
2472 cat 35 0 35 0 R ld.config.Q.txt
2453 cat 35 0 35 0 R ld.config.Q.txt
```

Start with the filetop entry point and reproduce the reported loop in the Android x86 emulator on the 4.14 kernel. Verify whether the displayed filename should be testfile and whether the append operations appear in the WRITES and W_Kb columns; done means both reported discrepancies are corrected and the behavior is confirmed against the example output.

Written by the indexing model from the issue text.