Unify the "go to bottom" logic of the two commit list contexts

The local commits and the sub-commits contexts had identical copies of
it. We are going to make it smarter, so make sure the copies don't
drift apart.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

pkg/gui/context/commit_list_goto_bottom.go

@@ -0,0 +1,23 @@
+package context
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/commands/models"
+	"github.com/samber/lo"
+)
+
+// Returns the index of the commit that the "go to bottom" command selects in a
+// list of commits
+func indexForGotoBottomInCommits(commits []*models.Commit, selectedIdx int) int {
+	if selectedIdx >= 0 && selectedIdx < len(commits)-1 {
+		if commits[selectedIdx+1].Status != models.StatusMerged {
+			_, idx, found := lo.FindIndexOf(commits, func(c *models.Commit) bool {
+				return c.Status == models.StatusMerged
+			})
+			if found {
+				return idx - 1
+			}
+		}
+	}
+
+	return len(commits) - 1
+}

pkg/gui/context/local_commits_context.go

@@ -520,18 +520,5 @@ func searchModelCommits(caseSensitive bool, commits []*models.Commit, columnPosi
 }
 
 func (self *LocalCommitsContext) IndexForGotoBottom() int {
-	commits := self.GetCommits()
-	selectedIdx := self.GetSelectedLineIdx()
-	if selectedIdx >= 0 && selectedIdx < len(commits)-1 {
-		if commits[selectedIdx+1].Status != models.StatusMerged {
-			_, idx, found := lo.FindIndexOf(commits, func(c *models.Commit) bool {
-				return c.Status == models.StatusMerged
-			})
-			if found {
-				return idx - 1
-			}
-		}
-	}
-
-	return self.list.Len() - 1
+	return indexForGotoBottomInCommits(self.GetCommits(), self.GetSelectedLineIdx())
 }

pkg/gui/context/sub_commits_context.go

@@ -269,18 +269,5 @@ func (self *SubCommitsContext) ModelSearchResults(searchStr string, caseSensitiv
 }
 
 func (self *SubCommitsContext) IndexForGotoBottom() int {
-	commits := self.GetCommits()
-	selectedIdx := self.GetSelectedLineIdx()
-	if selectedIdx >= 0 && selectedIdx < len(commits)-1 {
-		if commits[selectedIdx+1].Status != models.StatusMerged {
-			_, idx, found := lo.FindIndexOf(commits, func(c *models.Commit) bool {
-				return c.Status == models.StatusMerged
-			})
-			if found {
-				return idx - 1
-			}
-		}
-	}
-
-	return self.list.Len() - 1
+	return indexForGotoBottomInCommits(self.GetCommits(), self.GetSelectedLineIdx())
 }