yet another bugfix in selection management

Thanks Leonard Schütz for the report!

Failing scenario:
  click to move cursor
  hit backspace

First backspace wasn't being doing anything earlier.

main.lua

@@ -341,8 +341,8 @@ function App.mousepressed(x,y, mouse_button)
   for line_index,line in ipairs(Lines) do
     if line.mode == 'text' then
       if Text.in_line(line_index,line, x,y) then
-        -- delicate dance between cursor, selection and old cursor
-        -- manual tests:
+        -- delicate dance between cursor, selection and old cursor/selection
+        -- scenarios:
         --  regular press+release: sets cursor, clears selection
         --  shift press+release:
         --    sets selection to old cursor if not set otherwise leaves it untouched
@@ -396,6 +396,9 @@ function App.mousereleased(x,y, button)
             end
           end
           Old_cursor1, Old_selection1, Mousepress_shift = nil
+          if eq(Cursor1, Selection1) then
+            Selection1 = {}
+          end
           break
         end
       end

text_tests.lua

@@ -76,6 +76,7 @@ function test_click_with_mouse()
   App.run_after_mouse_click(Margin_left+8,Margin_top+5, 1)
   -- cursor moves
   check_eq(Cursor1.line, 1, 'F - test_click_with_mouse/cursor')
+  check_nil(Selection1.line, 'F - test_click_with_mouse/selection is empty to avoid perturbing future edits')
 end
 
 function test_click_with_mouse_on_empty_line()
@@ -334,24 +335,6 @@ function test_cursor_movement_without_shift_resets_selection()
   check_eq(Lines[1].data, 'abc', 'F - test_cursor_movement_without_shift_resets_selection/data')
 end
 
-function test_edit_after_click_resets_selection()
-  io.write('\ntest_edit_after_click_resets_selection')
-  -- display a line of text
-  App.screen.init{width=75, height=80}
-  Lines = load_array{'abc'}
-  Margin_right = 0; Margin_width = Margin_left
-  Cursor1 = {line=1, pos=1}
-  Screen_top1 = {line=1, pos=1}
-  Screen_bottom1 = {}
-  App.draw()
-  -- click past the end of it and hit enter
-  App.run_after_mouse_click(Margin_left+40,Margin_top+5, 1)
-  check(Selection1.line, 'F - test_edit_after_click_resets_selection/baseline')
-  App.run_after_keychord('return')
-  -- selection is reset since shift key is not pressed
-  check_nil(Selection1.line, 'F - test_edit_after_click_resets_selection')
-end
-
 function test_edit_deletes_selection()
   io.write('\ntest_edit_deletes_selection')
   -- display a line of text with some part selected