QFSFileEngine: minor code clarification

Change-Id: I44f30f827cdb8e841a43ac911327286db051a725
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/corelib/io/qfsfileengine.cpp

@@ -649,7 +649,8 @@ qint64 QFSFileEnginePrivate::readFdFh(char *data, qint64 len)
             result = QT_READ(fd, data + readBytes, chunkSize);
         } while (result > 0 && (readBytes += result) < len);
 
-        eof = !(result == -1);
+        // QT_READ (::read()) returns 0 to indicate end-of-file
+        eof = result == 0;
     }
 
     if (!eof && readBytes == 0) {