Ensure that the pcache1 cache size does not get so big that it overflows

the integer that is keeping track of the cache size.

FossilOrigin-Name: bf9d70fc2fde06a3f132270a26d4abe321687169066aff26ad9e92757c7f9ee4

src/pcache1.c

@@ -820,6 +820,9 @@ static void pcache1Cachesize(sqlite3_pcache *p, int nMax){
   if( pCache->bPurgeable ){
     PGroup *pGroup = pCache->pGroup;
     pcache1EnterMutex(pGroup);
+    if( nMax > 0xffff0000 - pGroup->nMaxPage + pCache->nMax ){
+      nMax = 0xffff0000 - pGroup->nMaxPage + pCache->nMax;
+    }
     pGroup->nMaxPage += (nMax - pCache->nMax);
     pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage;
     pCache->nMax = nMax;
@@ -838,7 +841,7 @@ static void pcache1Shrink(sqlite3_pcache *p){
   PCache1 *pCache = (PCache1*)p;
   if( pCache->bPurgeable ){
     PGroup *pGroup = pCache->pGroup;
-    int savedMaxPage;
+    unsigned int savedMaxPage;
     pcache1EnterMutex(pGroup);
     savedMaxPage = pGroup->nMaxPage;
     pGroup->nMaxPage = 0;