use constructor semantics to zero init the context pointer, avoid one…

… memory sanitizer warning

Signed-off-by: Kimball Thurston <kdt3rd@gmail.com>

src/lib/OpenEXR/ImfContext.cpp

@@ -106,12 +106,11 @@ class MemAttrStream : public OPENEXR_IMF_NAMESPACE::IStream
 ////////////////////////////////////////
 
 Context::Context ()
-    : _ctxt (new exr_context_t, [] (exr_context_t* todel) {
+    : _ctxt (new exr_context_t(), [] (exr_context_t* todel) {
         exr_finish (todel);
         delete todel;
     })
 {
-    *_ctxt = nullptr;
 }
 
 ////////////////////////////////////////