virfile: Fix virFileExists commentary

Arguably though, function returning only on success is a very
interesting, although quite impractical concept. Also, the errno isn't
and shouldn't be preserved in this case, since the errno can be directly
fed to the virReportSystemError.
Signed-off-by: NErik Skultety <eskultet@redhat.com>

src/util/virfile.c

@@ -1820,7 +1820,8 @@ virFileIsDir(const char *path)
  * virFileExists: Check for presence of file
  * @path: Path of file to check
  *
- * Returns if the file exists. Preserves errno in case it does not exist.
+ * Returns true if the file exists, false if it doesn't, setting errno
+ * appropriately.
  */
 bool
 virFileExists(const char *path)