[SYCL] Fix host-to-host copy during copyback (#1692)

Copyback is performed unconditionally during buffer destruction, so
it's possible for it to perform a copy from and to the same host
pointer. This patch adds a check for this scenario so that we don't rely
on undefined behaviour of std::memcpy.

Signed-off-by: Sergey Semenov <sergey.semenov@intel.com>

Author: sergey-semenov

sycl/source/detail/memory_manager.cpp

@@ -358,13 +358,15 @@ static void copyH2H(SYCLMemObjI *SYCLMemObj, char *SrcMem,
                         PI_INVALID_OPERATION);
   }
 
-  DstOffset[0] *= DstElemSize;
-  SrcOffset[0] *= SrcElemSize;
+  SrcMem += SrcOffset[0] * SrcElemSize;
+  DstMem += DstOffset[0] * DstElemSize;
+
+  if (SrcMem == DstMem)
+    return;
 
   size_t BytesToCopy =
       SrcAccessRange[0] * SrcElemSize * SrcAccessRange[1] * SrcAccessRange[2];
-
-  std::memcpy(DstMem + DstOffset[0], SrcMem + SrcOffset[0], BytesToCopy);
+  std::memcpy(DstMem, SrcMem, BytesToCopy);
 }
 
 // Copies memory between: host and device, host and host,