Invalid value handling

[vladinator1000]

We should handle errors when parsing a value with a missing closing brace:

.corrupt {
  color: hsla(120, 62.32%;
}

Related issue: #427

This aims to replicate this browser behavior

[vladinator1000]

This test currently fails, because the parsing result is Ok when it should be an error.

---- value_missing_closing_brace stdout ----
thread 'value_missing_closing_brace' panicked at 'called `Result::unwrap_err()` on an `Ok` value: StyleSheet { rules: CssRuleList([Style(StyleRule { selectors: SelectorList([Selector(.corrupt, specificity = 0x400)]), vendor_prefix: (empty), declarations: DeclarationBlock { important_declarations: [], declarations: [Unparsed(UnparsedProperty { property_id: Color, value: TokenList([Function(Function { name: Ident("hsla"), arguments: TokenList([Token(Number { has_sign: false, value: 120.0, int_value: Some(120) }), Token(Comma), Token(Percentage { has_sign: false, unit_value: 0.6232, int_value: None }), Token(Semicolon), Token(WhiteSpace(" ")), Token(CloseCurlyBracket)]) })]) })] }, rules: CssRuleList([]), loc: Location { source_index: 0, line: 1, column: 5 } })]), sources: [""], source_map_urls: [None], options: ParserOptions { filename: "", nesting: false, custom_media: false, css_modules: None, source_index: 0, error_recovery: false, warnings: None } }', tests/test_invalid_input.rs:15:67