Only try to display messages from valid lines

Attempting to prevent the following exception:

    Uncaught Error: No screen line exists when converting buffer row to screen row /Applications/Atom.app/Contents/Resources/app/src/display-buffer.js:932
      module.exports.DisplayBuffer.screenPositionForBufferPosition /Applications/Atom.app/Contents/Resources/app/src/display-buffer.js:932
      module.exports.Marker.getHeadScreenPosition /Applications/Atom.app/Contents/Resources/app/src/marker.js:211
      Marker /Applications/Atom.app/Contents/Resources/app/src/marker.js:45
      module.exports.DisplayBuffer.getMarker /Applications/Atom.app/Contents/Resources/app/src/display-buffer.js:1124
      module.exports.DisplayBuffer.markBufferRange /Applications/Atom.app/Contents/Resources/app/src/display-buffer.js:1156
      module.exports.Editor.markBufferRange /Applications/Atom.app/Contents/Resources/app/src/editor.js:1186
      LinterView.display linter-view.coffee:180
      LinterView.processMessage linter-view.coffee:159
      (anonymous function) linter-view.coffee:1
      (anonymous function) linter-view.coffee:142
      Linter.processMessage linter.coffee:150
      (anonymous function) linter.coffee:127
      BufferedProcess.triggerExitCallback /Applications/Atom.app/Contents/Resources/app/src/buffered-process.js:52
      (anonymous function) /Applications/Atom.app/Contents/Resources/app/src/buffered-process.js:59
      (anonymous function) /Applications/Atom.app/Contents/Resources/app/src/buffered-process.js:105
      EventEmitter.emit events.js:129
      (anonymous function) net.js:461

Test Plan:
Crossed fingers

lib/linter.coffee

@@ -145,7 +145,7 @@ class Linter
     messages = []
     regex = XRegExp @regex, @regexFlags
     XRegExp.forEach message, regex, (match, i) =>
-      messages.push(@createMessage(match))
+      messages.push(m) if m = @createMessage(match)
     , this
     callback messages
 
@@ -229,6 +229,13 @@ class Linter
     rowStart = decrementParse match.lineStart ? match.line
     rowEnd = decrementParse match.lineEnd ? match.line
 
+    # if this message purports to be from beyond the maximum line count,
+    # ignore it
+    maxRow = rowEnd ? rowStart
+    if maxRow > @editor.getLineCount()
+      log "ignoring #{match} - it's longer than the buffer"
+      return null
+
     match.col ?=  0
     unless match.colStart
       position = new Point(rowStart, match.col)