fix: Properly find wrapped lines in history buffer

[rivenirvana]

Off-by-one error in f412ec6. Kitty is failing to find the previous prompt when trying to page the last command output (via ctrl+shift+g) when the executed command is long enough that it wraps and the output is long enough to put the prompt in the history buffer. The result is either:

• Paged cmd output is empty; or
• Paged output contains cmd outputs from up to the first prompt that has a non-wrapping command; or
• The last wrapped line of the command is included in the paged output when paging via mouse (ctrl+shift+rclick)