Avoid checking a function name in the input

It may not be specified in lowercase.

Author: cdoublev

lib/parse/preprocess.js

@@ -192,11 +192,12 @@ function preParseCompoundSelector(node) {
         && !isColon(next)
         && findContext('function', node, node =>
             pseudos.logical[node.definition.name]
-            // ::part(name):not(type) must be valid (but match nothing)
-            && node.input.prev(1, 1)?.name?.toLowerCase() !== 'part'
             && findParent(
                 node,
-                node => node.definition.name === '<pseudo-compound-selector>',
+                node =>
+                    node.parent?.definition.name === '<pseudo-compound-selector>'
+                    // ::part(name):not(type) must be valid (but match nothing)
+                    && node.children[0].value[1][1].name !== 'part',
                 node => node.definition.name === '<subclass-selector>'))
     ) {
         return error(node)