PLain Text Editor: Remove list indentation

As it causes dashed lists to be formatted as
- i1
  - i2
Just do paragraph formatting.

Task-number: QTCREATORBUG-538
Initial-patch-by: Thorbjørn Lindeijer <thorbjorn.lindeijer@nokia.com>
(cherry picked from commit 2986ccafd2)

src/plugins/texteditor/plaintexteditor.cpp

@@ -109,11 +109,10 @@ void PlainTextEditor::indentBlock(QTextDocument *doc, QTextBlock block, QChar ty
         return;
 
     // Just use previous line.
-    // Skip non-alphanumerical characters when determining the indentation
-    // to enable writing bulleted lists whose items span several lines.
+    // Skip blank characters when determining the indentation
     int i = 0;
     while (i < previousText.size()) {
-        if (previousText.at(i).isLetterOrNumber()) {
+        if (!previousText.at(i).isSpace()) {
             const TextEditor::TabSettings &ts = tabSettings();
             ts.indentLine(block, ts.columnAt(previousText, i));
             break;