Fix a harmless compiler warning in lemon.c.

FossilOrigin-Name: 62959c0ce3a2c486ebd82e6511efad0412b944a0
diff --git a/tool/lemon.c b/tool/lemon.c
index ac08250..58f1388 100644
--- a/tool/lemon.c
+++ b/tool/lemon.c
@@ -3458,7 +3458,7 @@
         break;
       }
       hash++;
-      if( hash>=arraysize ) hash = 0;
+      if( hash>=(unsigned)arraysize ) hash = 0;
     }
     if( types[hash]==0 ){
       sp->dtnum = hash + 1;