m_pColorSpace can not be NULL for image object with DCTDecode filter

BUG=411842
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/792113003
diff --git a/core/src/fpdfapi/fpdf_render/fpdf_render_loadimage.cpp b/core/src/fpdfapi/fpdf_render/fpdf_render_loadimage.cpp
index f053e55..1637655 100644
--- a/core/src/fpdfapi/fpdf_render/fpdf_render_loadimage.cpp
+++ b/core/src/fpdfapi/fpdf_render/fpdf_render_loadimage.cpp
@@ -504,6 +504,9 @@
 }
 DIB_COMP_DATA* CPDF_DIBSource::GetDecodeAndMaskArray(FX_BOOL& bDefaultDecode, FX_BOOL& bColorKey)
 {
+    if (m_pColorSpace == NULL) {
+        return NULL;
+    }
     DIB_COMP_DATA* pCompData = FX_Alloc(DIB_COMP_DATA, m_nComponents);
     if (pCompData == NULL) {
         return NULL;