[Rules] Fix endless loop on unknown {...} in rules on ESP8266

In parse_string_commands() the branch without FEATURE_EXTENDED_STRING_FUNCTIONS
masked '{' and '}' in the whole line instead of in replacement (regression from
4e191fc5b). The following line.replace() put the unmasked braces back, so
get_next_inner_bracket() found them again and the loop never ended
(SW watchdog / exception reset). Mask replacement, as before 4e191fc5b.

Fixes #5653

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/src/ESPEasyCore/ESPEasyRules.cpp

@@ -884,8 +884,8 @@ void parse_string_commands(String& line) {
         #if FEATURE_EXTENDED_STRING_FUNCTIONS
         hideMasked(replacement, mustReplaceMaskedChars); // apply
         #else // if FEATURE_EXTENDED_STRING_FUNCTIONS
-        line.replace('{', static_cast<char>(0x02));
-        line.replace('}', static_cast<char>(0x03));
+        replacement.replace('{', static_cast<char>(0x02));
+        replacement.replace('}', static_cast<char>(0x03));
         #endif // if FEATURE_EXTENDED_STRING_FUNCTIONS
       }