Editor code: tidy up BOOLs,NULLs and overrides pt4.

A few 'typedefs' replaced by 'using's
This shouldn't have any functional changes at all, just c++17 modernization
It's a part 4 of a split #2847

Signed-off-by: Nemerle <nemerle5+git@gmail.com>

Code/Editor/Util/MemoryBlock.cpp

@@ -18,7 +18,7 @@
 
 //////////////////////////////////////////////////////////////////////////
 CMemoryBlock::CMemoryBlock()
-    : m_buffer(0)
+    : m_buffer(nullptr)
     , m_size(0)
     , m_uncompressedSize(0)
     , m_owns(false)
@@ -54,7 +54,7 @@ CMemoryBlock& CMemoryBlock::operator=(const CMemoryBlock& mem)
     }
     else
     {
-        m_buffer = 0;
+        m_buffer = nullptr;
         m_size = 0;
         m_owns = false;
     }
@@ -104,7 +104,7 @@ bool CMemoryBlock::Allocate(int size, int uncompressedSize)
     m_size = size;
     m_uncompressedSize = uncompressedSize;
     // Check if allocation failed.
-    if (m_buffer == 0)
+    if (m_buffer == nullptr)
     {
         return false;
     }
@@ -118,7 +118,7 @@ void CMemoryBlock::Free()
     {
         free(m_buffer);
     }
-    m_buffer = 0;
+    m_buffer = nullptr;
     m_owns = false;
     m_size = 0;
     m_uncompressedSize = 0;