Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: mathieucarbou

src/WebRequest.cpp

@@ -540,6 +540,18 @@ bool AsyncWebServerRequest::_parseReqHeader() {
           }
           // Strip the surrounding quotes; content between them is the boundary.
           _boundary = _boundary.substring(1, endQuote);
+
+          // Unescape quoted-pair sequences so the boundary matches the actual bytes on the wire.
+          String unescaped;
+          unescaped.reserve(_boundary.length());
+          for (size_t i = 0; i < _boundary.length(); ++i) {
+            char c = _boundary.charAt(i);
+            if (c == '\\' && (i + 1) < _boundary.length()) {
+              c = _boundary.charAt(++i);
+            }
+            unescaped += c;
+          }
+          _boundary = unescaped;
         } else {
           // Token form: the value ends at the next ';' (start of the next
           // parameter) or at the end of the header field.