compiler: invalid handling of variables imported from template files and used in macros

[zapateo]

The issue #852 was fixed and tests were added, but these tests do not seem to be extensive enough, and therefore panics occur in the runtime (and possibly in the disassembler).

To reproduce such panics:

"https://github.com/open2b/scriggo/issues/852 - Additional tests #1": {
	sources: fstest.Files{
		"index.html":    `{% import pkg "imported.html" %}a{% macro M %}b{{ pkg.V }}c{% end macro %}d{{ M() }}`,
		"imported.html": `{% var V int %}`,
	},
	expectedOut: "TODO",
},

"https://github.com/open2b/scriggo/issues/852 - Additional tests #2": {
	sources: fstest.Files{
		"index.html":    `{% import pkg "imported.html" %}a{% macro M %}b{{ pkg.V }}c{% end macro %}d{{ M() }}`,
		"imported.html": `{% var V int = 42 %}`,
	},
	expectedOut: "TODO",
},