fix Rcpp -Wformat-security warning

for howto, see RcppCore/Rcpp#1287

Author: edzer

src/RcppExports.cpp

@@ -1352,7 +1352,7 @@ RcppExport SEXP _sf_CPL_read_wkb(SEXP wkb_listSEXP, SEXP EWKBSEXP, SEXP spatiali
     if (rcpp_isError_gen) {
         SEXP rcpp_msgSEXP_gen = Rf_asChar(rcpp_result_gen);
         UNPROTECT(1);
-        Rf_error(CHAR(rcpp_msgSEXP_gen));
+        Rf_error("%s", CHAR(rcpp_msgSEXP_gen));
     }
     UNPROTECT(1);
     return rcpp_result_gen;
@@ -1387,7 +1387,7 @@ RcppExport SEXP _sf_CPL_write_wkb(SEXP sfcSEXP, SEXP EWKBSEXP) {
     if (rcpp_isError_gen) {
         SEXP rcpp_msgSEXP_gen = Rf_asChar(rcpp_result_gen);
         UNPROTECT(1);
-        Rf_error(CHAR(rcpp_msgSEXP_gen));
+        Rf_error("%s", CHAR(rcpp_msgSEXP_gen));
     }
     UNPROTECT(1);
     return rcpp_result_gen;