perf(dpx): use default_init_vector to speed up allocation for internal buffers (AcademySoftwareFoundation#5183)

This just avoids needing to zero out the allocated buffer, since we know
we are allocating it merely to write into it. Uninitialized contents is
ok and faster.

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

src/dpx.imageio/dpxinput.cpp

@@ -57,9 +57,9 @@ class DPXInput final : public ImageInput {
     int m_subimage;
     InStream* m_stream = nullptr;
     dpx::Reader m_dpx;
-    std::vector<unsigned char> m_userBuf;
+    default_init_vector<unsigned char> m_userBuf;
+    default_init_vector<unsigned char> m_decodebuf;  // temporary decode buffer
     bool m_rawcolor;
-    std::vector<unsigned char> m_decodebuf;  // temporary decode buffer
 
     /// Reset everything to initial state
     ///