One more MSVC fix related to module only name apearing without function name

include/boost/stacktrace/detail/frame_msvc.ipp

@@ -236,12 +236,17 @@ public:
             return result;
         }
 
-        // If 'delimiter' is equal to 'std::string::npos' then we have only module name.
         const std::size_t delimiter = result.find_first_of('!');
         if (module_name) {
             *module_name = result.substr(0, delimiter);
         }
 
+        if (delimiter == std::string::npos) {
+            // If 'delimiter' is equal to 'std::string::npos' then we have only module name.
+            result.clear();
+            return result;
+        }
+
         result = minwg_demangling_workaround(
             result.substr(delimiter + 1)
         );