Fix pressing escape after clicking in diff view (#3828)

- **PR Description**

When clicking in a single-file diff view to enter staging (or custom
patch editing, when coming from the commit files panel), you needed to
press escape twice to exit, where the first press would seemingly do
nothing.

pkg/gui/patch_exploring/state.go

@@ -112,7 +112,7 @@ func (s *State) SelectingHunk() bool {
 }
 
 func (s *State) SelectingRange() bool {
-	return s.selectMode == RANGE
+	return s.selectMode == RANGE && (s.rangeIsSticky || s.rangeStartLineIdx != s.selectedLineIdx)
 }
 
 func (s *State) SelectingLine() bool {