Fixing rs crash when no texture is bound.

Change-Id: I2c15106f50de995c63691f27e2c4d89dbffc758e
diff --git a/libs/rs/driver/rsdProgram.cpp b/libs/rs/driver/rsdProgram.cpp
index 39b3805..27a6663 100644
--- a/libs/rs/driver/rsdProgram.cpp
+++ b/libs/rs/driver/rsdProgram.cpp
@@ -44,6 +44,9 @@
 static void SyncProgramConstants(const Context *rsc, const Program *p) {
     for (uint32_t ct=0; ct < p->mHal.state.texturesCount; ct++) {
         const Allocation *a = p->mHal.state.textures[ct].get();
+        if (!a) {
+            continue;
+        }
         DrvAllocation *drvAlloc = (DrvAllocation *)a->mHal.drv;
         if (drvAlloc->uploadDeferred) {
             rsdAllocationSyncAll(rsc, a, RS_ALLOCATION_USAGE_SCRIPT);