Consume consecutive delimiters at beginning of refilled buffer

This change makes sure that the consecutive delimiters at the
beginning of the just refilled buffer are consumed.

Previously, if there were consecutive delimiters at the beginning
of the just refilled buffer, they were not being consumed and were
causing parsing errors. This was also causing fatal exceptions.

```
04-22 12:37:53.077   607   707 E AndroidRuntime: *** FATAL EXCEPTION IN SYSTEM PROCESS: CachedAppOptimizerThread
04-22 12:37:53.077   607   707 E AndroidRuntime: java.lang.NumberFormatException: invalid long: READ
04-22 12:37:53.077   607   707 E AndroidRuntime: 	at com.android.internal.util.ProcFileReader.invalidLong(ProcFileReader.java:238)
04-22 12:37:53.077   607   707 E AndroidRuntime: 	at com.android.internal.util.ProcFileReader.parseAndConsumeLong(ProcFileReader.java:220)
04-22 12:37:53.077   607   707 E AndroidRuntime: 	at com.android.internal.util.ProcFileReader.nextLong(ProcFileReader.java:183)
04-22 12:37:53.077   607   707 E AndroidRuntime: 	at com.android.internal.util.ProcFileReader.nextLong(ProcFileReader.java:172)
04-22 12:37:53.077   607   707 E AndroidRuntime: 	at com.android.internal.util.ProcFileReader.nextInt(ProcFileReader.java:246)
04-22 12:37:53.077   607   707 E AndroidRuntime: 	at com.android.internal.os.ProcLocksReader.handleBlockingFileLocks(ProcLocksReader.java:111)
04-22 12:37:53.077   607   707 E AndroidRuntime: 	at com.android.server.am.CachedAppOptimizer$FreezeHandler.handleMessage(CachedAppOptimizer.java:2267)
04-22 12:37:53.077   607   707 E AndroidRuntime: 	at android.os.Handler.dispatchMessage(Handler.java:107)
04-22 12
```

Bug: 336208153
Bug: 338416108
Bug: 331988929
Test: atest --host-unit-test-only -c  ProcFileReaderTest
Change-Id: I12813fa204d53d53687ffe6e8e3c0a85595b7e25