show any error after switching to source editor

Dependencies

• [2] BYKXF3YY bugfix: draw menu after everything else
• [*] KKMFQDR4 editing source code from within the app
• [*] OTIBCAUJ love2d scaffold

Change contents

• edit in source.lua at line 255
  [2.37]

  [4.173129]
  + if Error_message then

  + local height = math.min(20*Editor_state.line_height, App.screen.height*0.2)

  + App.color{r=0.8,g=0,b=0}

  + love.graphics.rectangle('fill', 150, App.screen.height - height-10, App.screen.width, height+10)

  + App.color{r=0,g=0,b=0}

  + love.graphics.print(Error_message, 150+10, App.screen.height - height)

  + end
• edit in main.lua at line 186
  [4.189132]

  [4.189132]
  + -- preserve any Error_message when going from run to source
• edit in main.lua at line 191
  [4.189284]

  [4.189284]
  + Error_message = nil