Fix less-than-zero checks on unsigned numbers
diff --git a/library/ripemd160.c b/library/ripemd160.c
index 73da510..4781a7d 100644
--- a/library/ripemd160.c
+++ b/library/ripemd160.c
@@ -280,7 +280,7 @@
     size_t fill;
     uint32_t left;
 
-    if( ilen <= 0 )
+    if( ilen == 0 )
         return;
 
     left = ctx->total[0] & 0x3F;