[Bug] not support going to find previous character by `,` in view mode

[zzhixin]

Steps to reproduce and Desired Effect (standard in vim editor)

1. Type text: This is a sentence. This is another sentence;
2. Get into normal mode;
3. Go to begining of the line: press 0;
4. Get into view mode: press v;
5. Find next .: press f.;
6. Find next .: press ;;
7. (Oops, goes too much), Find previous .: press ,.

Things goes wrong in step 7: failed to go back.