ExecuteJavascript crashes when startLine=0/None. Update docs.

Upstream issue: https://magpcss.org/ceforum/viewtopic.php?f=6&t=14626

Also update documentation (Browser and Frame objects) with scriptUrl="" and startLine=1. Currently:
```
scriptUrl=None	string
startLine=None	int
```
