disallow textSize() <= 0 (fixes #3110)

core/src/processing/core/PGraphics.java

@@ -4131,6 +4131,12 @@ public class PGraphics extends PImage implements PConstants {
    * @see PGraphics#textFont(PFont)
    */
   public void textSize(float size) {
+    // https://github.com/processing/processing/issues/3110
+    if (size <= 0) {
+      System.err.println("textSize(" + size + ") ignored: " +
+                         "the text size must be larger than zero");
+      return;
+    }
     if (textFont == null) {
       defaultFontOrDeath("textSize", size);
     }

core/todo.txt

@@ -8,6 +8,8 @@ X   mostly getting away from this
 X bezierSegment() function to do equal-length segments
 X   https://github.com/processing/processing/issues/2919
 X   handled instead as an example
+X add warning message when a negative textSize() is used
+X   https://github.com/processing/processing/issues/3110
 
 _ dragging sketch window hides it
 _   https://github.com/processing/processing/issues/3092