Fix scrolling hunk into view when selecting next hunk

If the hunk to be selected was partially scrolled offscreen, the view wouldn't
scroll enough to make it completely visible (the last line of the hunk was still
offscreen).

This is only a minimal fix for a pressing problem. The code to handle scrolling
after selection changes has lots of problems, and is also inconsistent between
list views and the patch explorer, but cleaning this up needs more time than I
have right now.

Author: stefanhaller

pkg/gui/patch_exploring/focus.go

@@ -22,7 +22,7 @@ func calculateNewOriginWithNeededAndWantedIdx(currentOrigin int, bufferHeight in
 		allowedChange := bottom - needToSeeIdx
 		return origin - min(requiredChange, allowedChange)
 	} else if wantToSeeIdx >= bottom {
-		requiredChange := wantToSeeIdx - bottom
+		requiredChange := wantToSeeIdx + 1 - bottom
 		allowedChange := needToSeeIdx - origin
 		return origin + min(requiredChange, allowedChange)
 	}