fix: spgemm negative maxAllocSize

Author: artemiipatov

src/GraphBLAS-sharp.Backend/Objects/ClContextExtensions.fs

@@ -47,6 +47,6 @@ module ClContextExtensions =
 
             Cl
                 .GetDeviceInfo(this.ClDevice.Device, OpenCL.Net.DeviceInfo.MaxMemAllocSize, error)
-                .CastTo<int>()
+                .CastTo<uint64>()
             |> uint64
             |> ((*) 1UL<Byte>)

src/GraphBLAS-sharp.Backend/Operations/SpGeMM/Expand.fs

@@ -447,7 +447,9 @@ module internal Expand =
             let generalLength, segmentLengths =
                 getSegmentPointers processor leftMatrix.Columns rightMatrixRowsNNZ
 
-            if generalLength < maxAllocSize then
+            if generalLength = 0 then
+                None
+            elif generalLength < maxAllocSize then
                 segmentLengths.Free processor
 
                 runOneStep processor allocationMode leftMatrix rightMatrixRowsNNZ rightMatrix