fix return value of range eraser in Vector

Author: yixuan

inst/include/Rcpp/vector/Vector.h

@@ -894,13 +894,13 @@ class Vector :
         iterator target_it = target.begin() ;
 
         SEXP names = RCPP_GET_NAMES(Storage::get__()) ;
-        iterator result ;
+        int result = 0;
         if( Rf_isNull(names) ){
             int i=0;
             for( ; it < first; ++it, ++target_it, i++ ){
                 *target_it = *it ;
             }
-            result = begin() + i + 1 ;
+            result = i;
             for( it = last ; it < this_end; ++it, ++target_it ){
                 *target_it = *it ;
             }
@@ -911,7 +911,7 @@ class Vector :
                 *target_it = *it ;
                 SET_STRING_ELT( newnames, i, STRING_ELT(names, i ) );
             }
-            result = begin() + i + 1 ;
+            result = i;
             for( it = last ; it < this_end; ++it, ++target_it, i++ ){
                 *target_it = *it ;
                 SET_STRING_ELT( newnames, i, STRING_ELT(names, i + nremoved ) );
@@ -920,7 +920,7 @@ class Vector :
         }
         Storage::set__( target.get__() ) ;
 
-        return result ;
+        return begin() + result;
 
     }