Fix harmless compiler warnings in the progress callback logic.

FossilOrigin-Name: 908141d5bf7a9ad8f40c2332476847733eca7fdc
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 5e3b4d0..d1d73cd 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -936,7 +936,7 @@
 #ifndef SQLITE_OMIT_PROGRESS_CALLBACK
   int (*xProgress)(void *);     /* The progress callback */
   void *pProgressArg;           /* Argument to the progress callback */
-  int nProgressOps;             /* Number of opcodes for progress callback */
+  unsigned nProgressOps;        /* Number of opcodes for progress callback */
 #endif
 #ifndef SQLITE_OMIT_VIRTUALTABLE
   int nVTrans;                  /* Allocated size of aVTrans */