use nprot and reference stop_sym (closes #951)

Author: eddelbuettel

ChangeLog

@@ -1,3 +1,8 @@
+2019-03-18  Dirk Eddelbuettel  <edd@debian.org>
+
+	* inst/include/Rcpp/macros/macros.h (END_RCPP_RETURN_ERROR): Add
+	UNPROTECT to reference nprot, also check for stop_sym
+
 2019-03-17  Dirk Eddelbuettel  <edd@debian.org>
 
         * DESCRIPTION: Release 1.0.1

inst/include/Rcpp/macros/macros.h

@@ -98,7 +98,10 @@
   catch (...) {                                                                \
     return string_to_try_error("c++ exception (unknown reason)");              \
   }                                                                            \
-  return R_NilValue;
+  UNPROTECT(nprot);                                                            \
+  return R_NilValue;                                                           \
+  if (stop_sym == R_NilValue) /* never reached but */                          \
+    return R_NilValue;        /* suppresses warning*/
 #endif
 
 #define Rcpp_error(MESSAGE) throw Rcpp::exception(MESSAGE, __FILE__, __LINE__)