fix: invalid processing of leading and trailing comments

[ykolbin]

There is an issue with preferred trailing comment processing (preferTrailingComment = true), if the next field contains a leading comment.

message A {
    // Field with both comments
    string field1 = 1; // trailing comment
 
    // Field with leading comment
    string field2 = 2;
}

Actual Result:
field1.comment = "Field with both comments"
field2.comment = "field2 trailing comment"

Expected Result:
field1.comment = "field1 trailing comment"
field2.comment = "field2 trailing comment"

[ykolbin]

Alexander Gennadievich (@alexander-fenster), could you help with review? 🙂

[alexander-fenster]

Hi @ykolbin, nice to see you here :) Sure, we'll take care of this on our next review meeting within a week or so (it will require some staring in the code to figure out what's going on).