Make setPlaceholders behavior consistent with setRelationalPlaceholders

Relational placeholders require an underscore after the identifier to be considered valid. For example: `%rel_chatchat_%` is valid but `%rel_chatchat%` is not. Normal placeholders did not require this and `%chatchat%` worked the same as `%chatchat_%`.

src/main/java/me/clip/placeholderapi/replacer/CharsReplacer.java

@@ -67,10 +67,14 @@ public final class CharsReplacer implements Replacer {
           hadSpace = true;
           break;
         }
-        if (p == closure.tail) {
+        if (p == closure.tail && identified) {
           invalid = false;
           break;
         }
+        if (p == closure.tail) {
+          identifier.append(p);
+          break;
+        }
 
         if (p == '_' && !identified) {
           identified = true;