Fix some compiler warnings in the MSVC build.

FossilOrigin-Name: 1f5662b7db5d623c8d99c45a8d97a0aa4427593f
diff --git a/src/expr.c b/src/expr.c
index fd21eb5..33864b2 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -566,7 +566,7 @@
           db->aLimit[SQLITE_LIMIT_VARIABLE_NUMBER]);
     }
     if( i>pParse->nVar ){
-      pParse->nVar = i;
+      pParse->nVar = (int)i;
     }
   }else{
     /* Wildcards like ":aaa", "$aaa" or "@aaa".  Reuse the same variable