Check if pad name can be used as element id (#133)

If pad name has any special symbols or does not start from letter,
replace pad name with global identifier.

Author: linev

scripts/JSRootPainter.js

@@ -4376,8 +4376,11 @@
       this.pad = pad;
       this.iscan = iscan; // indicate if working with canvas
       this.this_pad_name = "";
-      if (!this.iscan && (pad !== null) && ('fName' in pad))
+      if (!this.iscan && (pad !== null) && ('fName' in pad)) {
          this.this_pad_name = pad.fName.replace(" ", "_"); // avoid empty symbol in pad name
+         var regexp = new RegExp("^[A-Za-z][A-Za-z0-9_]*$");
+         if (!regexp.test(this.this_pad_name)) this.this_pad_name = 'jsroot_pad_' + JSROOT.id_counter++;
+      }
       this.painters = []; // complete list of all painters in the pad
       this.has_canvas = true;
    }