Get Context Fortification

[korgon]

The recent change to getContext (0.62.0) adding "auto-detect variables for evaluation list" had an unexpected side effect of generating errors when the auto-detected variable was a Javascript keyword.

Example:

format = "<span class=money>${{amount}}</span>";

The variable class was being extracted and added to the evaluate list.

Changes:

1. prevent extracting variables within quotes
2. adding a keyword set to ensure we never attempt to assign variables using these keywords
3. wrapping evaluation in a try/catch to ensure Snap execution continues