str: fix underflow in rtraverse() on empty strings

Fix possible str underflow with empty strings.

Reported-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: msune

CHANGELOG.md

@@ -19,6 +19,7 @@ Legend:
 - [B] str: align `cdada_str()` invalid-handle behavior with API docs (return `NULL`, not empty string)
 - [B] bbitmap: make `cdada_bbitmap_dump()` set `size_used` in buffered paths too
 - [B] bbitmap: fix corrupted BSD license header in `bbitmap.h`
+- [B] str: fix uint32_t underflow in `cdada_str_rtraverse()` on empty strings
 - [O] tests: add coverage for `cdada_strerr()` valid, boundary and high invalid values
 - [O] tests: add `oom_create_test` coverage for create paths (`list`, `map`, `queue`, `set`, `stack`, `str`, `bbitmap`)
 - [O] tests: add coverage for `cdada_str_replace_all()` empty-match invalid input and self-overlap replacement

src/str.cc

@@ -93,6 +93,8 @@ int cdada_str_rtraverse(const cdada_str_t* str, cdada_str_it func,
 
 	try{
 		std::string::const_reverse_iterator it;
+		if(s.empty())
+			return CDADA_SUCCESS;
 		uint32_t pos = s.length()-1;
 		for(it = s.rbegin(); it != s.rend(); ++it){
 			(*func)(str, *it, pos, opaque);