Add logic to getNextSelectionRange so that selection remains at bottom when last line is staged

Co-Authored-By: Vanessa Yuen <[email protected]>

Author: kuychaco

lib/models/patch/multi-file-patch.js

@@ -162,20 +162,30 @@ export default class MultiFilePatch {
 
     let newSelectionRow = 0;
     let remainingChangedLines = lastSelectionIndex;
+
+    let foundRow = false;
+    let lastChangedRow;
+
     // counts the same number of lines but backwards in the new patch.
     patchLoop: for (const filePatch of this.getFilePatches()) {
       for (const hunk of filePatch.getHunks()) {
         for (const change of hunk.getChanges()) {
           if (remainingChangedLines < change.bufferRowCount()) {
             newSelectionRow = change.getStartBufferRow() + remainingChangedLines;
+            foundRow = true;
             break patchLoop;
           } else {
             remainingChangedLines -= change.bufferRowCount();
+            lastChangedRow = change.getEndBufferRow();
           }
         }
       }
     }
 
+    if (!foundRow) { // the selected line was the last changed line
+      newSelectionRow = lastChangedRow;
+    }
+
     return Range.fromObject([[newSelectionRow, 0], [newSelectionRow, Infinity]]);
   }