typos in keywords txt can break syntax highlighting

fixes #1269

Author: Federico Fissore

app/src/processing/app/syntax/PdeKeywords.java

@@ -98,7 +98,7 @@ static private void getKeywords(InputStream input) throws Exception {
         //String htmlFilename = second.substring(tab + 1).trim();
         String coloring = pieces[1].trim();
 
-        if (coloring.length() > 0) {
+        if (coloring.length() > 0 && Character.isDigit(coloring.charAt(coloring.length() - 1))) {
           // text will be KEYWORD or LITERAL
           boolean isKey = (coloring.charAt(0) == 'K');
           // KEYWORD1 -> 0, KEYWORD2 -> 1, etc