Add checks for mmap and getSpace

Signed-off-by: John Falkowski <john.falkowski@intel.com>

shared/source/command_stream/linear_stream.h

@@ -62,6 +62,7 @@ inline void *LinearStream::getSpace(size_t size) {
         cmdContainer->closeAndAllocateNextCommandBuffer();
     }
     UNRECOVERABLE_IF(sizeUsed + size > maxAvailableSpace);
+    UNRECOVERABLE_IF(reinterpret_cast<int64_t>(buffer) <= 0);
     auto memory = ptrOffset(buffer, sizeUsed);
     sizeUsed += size;
     return memory;