get rid of a 32-bit Windows build warning

Warning was (twice for same line):
db\pipeline\expression.cpp(2612): warning C4244: 'argument' : conversion from '__int64' to 'unsigned int', possible loss of data

1 files changed, 2 insertions, 2 deletions

diff --git a/db/pipeline/expression.cpp b/db/pipeline/expression.cpp
index 8fb7a5fe247..b3caefcf899 100755
--- a/db/pipeline/expression.cpp
+++ b/db/pipeline/expression.cpp
@@ -2605,8 +2605,8 @@ namespace mongo {
 		(pLength->getType() == NumberInt 

 		 || pLength->getType() == NumberLong 

 		 || pLength->getType() == NumberDouble));

-        long long lower = pLower->coerceToLong();

-        long long length = pLength->coerceToLong();

+        string::size_type lower = static_cast< string::size_type >( pLower->coerceToLong() );

+        string::size_type length = static_cast< string::size_type >( pLength->coerceToLong() );

         return Value::createString( str.substr(lower, length) );

     }