Initialize tilesAfterReorder properly (#3984)

It may contain a garbage value, and if it is large then
updateNeighborListSize does not force reorder atoms after 25 steps
in extremal cases.

platforms/cuda/src/CudaNonbondedUtilities.cpp

@@ -64,7 +64,7 @@ private:
 };
 
 CudaNonbondedUtilities::CudaNonbondedUtilities(CudaContext& context) : context(context), useCutoff(false), usePeriodic(false), anyExclusions(false), usePadding(true),
-        blockSorter(NULL), pinnedCountBuffer(NULL), forceRebuildNeighborList(true), lastCutoff(0.0), groupFlags(0), canUsePairList(true) {
+        blockSorter(NULL), pinnedCountBuffer(NULL), forceRebuildNeighborList(true), lastCutoff(0.0), groupFlags(0), canUsePairList(true), tilesAfterReorder(0) {
     // Decide how many thread blocks to use.
 
     string errorMessage = "Error initializing nonbonded utilities";
@@ -423,7 +423,7 @@ void CudaNonbondedUtilities::computeInteractions(int forceGroups, bool includeFo
 bool CudaNonbondedUtilities::updateNeighborListSize() {
     if (!useCutoff)
         return false;
-    if (context.getStepsSinceReorder() == 0)
+    if (context.getStepsSinceReorder() == 0 || tilesAfterReorder == 0)
         tilesAfterReorder = pinnedCountBuffer[0];
     else if (context.getStepsSinceReorder() > 25 && pinnedCountBuffer[0] > 1.1*tilesAfterReorder)
         context.forceReorder();

platforms/opencl/src/OpenCLNonbondedUtilities.cpp

@@ -56,7 +56,7 @@ private:
 };
 
 OpenCLNonbondedUtilities::OpenCLNonbondedUtilities(OpenCLContext& context) : context(context), useCutoff(false), usePeriodic(false), anyExclusions(false), usePadding(true),
-        blockSorter(NULL), pinnedCountBuffer(NULL), pinnedCountMemory(NULL), forceRebuildNeighborList(true), lastCutoff(0.0), groupFlags(0) {
+        blockSorter(NULL), pinnedCountBuffer(NULL), pinnedCountMemory(NULL), forceRebuildNeighborList(true), lastCutoff(0.0), groupFlags(0), tilesAfterReorder(0) {
     // Decide how many thread blocks and force buffers to use.
 
     deviceIsCpu = (context.getDevice().getInfo<CL_DEVICE_TYPE>() == CL_DEVICE_TYPE_CPU);
@@ -395,7 +395,7 @@ void OpenCLNonbondedUtilities::computeInteractions(int forceGroups, bool include
 bool OpenCLNonbondedUtilities::updateNeighborListSize() {
     if (!useCutoff)
         return false;
-    if (context.getStepsSinceReorder() == 0)
+    if (context.getStepsSinceReorder() == 0 || tilesAfterReorder == 0)
         tilesAfterReorder = pinnedCountMemory[0];
     else if (context.getStepsSinceReorder() > 25 && pinnedCountMemory[0] > 1.1*tilesAfterReorder)
         context.forceReorder();