Always check CFX_RenderDevice::CreateCompatibleBitmap() return value

By checking the return value from CreateCompatibleBitmap(), there is no
need to do a separate GetBuffer() check in
CPDF_RenderStatus::GetBackdrop(). Fix some nits there as well.

In CPDF_DeviceBuffer::OutputToDevice(), prevent a potential crash in
case CreateCompatibleBitmap() fails.

Bug: pdfium:2047
Change-Id: Ide7a6276de23339dec578bae2d1d8dfa3233770b
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/111993
Reviewed-by: Nigi <nigi@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>

core/fpdfapi/render/cpdf_devicebuffer.cpp

diff --git a/core/fpdfapi/render/cpdf_devicebuffer.cpp b/core/fpdfapi/render/cpdf_devicebuffer.cpp
index 5bf308a..61611b2 100644
--- a/core/fpdfapi/render/cpdf_devicebuffer.cpp
+++ b/core/fpdfapi/render/cpdf_devicebuffer.cpp
@@ -82,8 +82,10 @@
     return;
   }
   auto pBuffer = pdfium::MakeRetain<CFX_DIBitmap>();
-  m_pDevice->CreateCompatibleBitmap(pBuffer, m_pBitmap->GetWidth(),
-                                    m_pBitmap->GetHeight());
+  if (!m_pDevice->CreateCompatibleBitmap(pBuffer, m_pBitmap->GetWidth(),
+                                         m_pBitmap->GetHeight())) {
+    return;
+  }
   m_pContext->GetBackground(m_pDevice, m_pObject, nullptr, m_Matrix);
   pBuffer->CompositeBitmap(0, 0, pBuffer->GetWidth(), pBuffer->GetHeight(),
                            m_pBitmap, 0, 0, BlendMode::kNormal, nullptr, false);

core/fpdfapi/render/cpdf_renderstatus.cpp

diff --git a/core/fpdfapi/render/cpdf_renderstatus.cpp b/core/fpdfapi/render/cpdf_renderstatus.cpp
index 39101f0..72aadce 100644
--- a/core/fpdfapi/render/cpdf_renderstatus.cpp
+++ b/core/fpdfapi/render/cpdf_renderstatus.cpp
@@ -701,21 +701,19 @@
   int width = bbox.Width();
   int height = bbox.Height();
   auto pBackdrop = pdfium::MakeRetain<CFX_DIBitmap>();
-  if (bBackAlphaRequired && !m_bDropObjects)
-    pBackdrop->Create(width, height, FXDIB_Format::kArgb);
-  else
-    m_pDevice->CreateCompatibleBitmap(pBackdrop, width, height);
+  if (bBackAlphaRequired && !m_bDropObjects) {
+    if (!pBackdrop->Create(width, height, FXDIB_Format::kArgb)) {
+      return nullptr;
+    }
+  } else {
+    if (!m_pDevice->CreateCompatibleBitmap(pBackdrop, width, height)) {
+      return nullptr;
+    }
+  }
 
-  if (pBackdrop->GetBuffer().empty())
-    return nullptr;
-
-  bool bNeedDraw;
-  if (pBackdrop->IsAlphaFormat())
-    bNeedDraw = !(m_pDevice->GetRenderCaps() & FXRC_ALPHA_OUTPUT);
-  else
-    bNeedDraw = !(m_pDevice->GetRenderCaps() & FXRC_GET_BITS);
-
-  if (!bNeedDraw) {
+  const int cap_to_check =
+      pBackdrop->IsAlphaFormat() ? FXRC_ALPHA_OUTPUT : FXRC_GET_BITS;
+  if (m_pDevice->GetRenderCaps() & cap_to_check) {
     m_pDevice->GetDIBits(pBackdrop, bbox.left, bbox.top);
     return pBackdrop;
   }

core/fxge/cfx_renderdevice.h

diff --git a/core/fxge/cfx_renderdevice.h b/core/fxge/cfx_renderdevice.h
index b7ce809..8b45ef8 100644
--- a/core/fxge/cfx_renderdevice.h
+++ b/core/fxge/cfx_renderdevice.h
@@ -64,9 +64,9 @@
   int GetDeviceCaps(int id) const;
   RetainPtr<CFX_DIBitmap> GetBitmap() const;
   void SetBitmap(const RetainPtr<CFX_DIBitmap>& pBitmap);
-  bool CreateCompatibleBitmap(const RetainPtr<CFX_DIBitmap>& pDIB,
-                              int width,
-                              int height) const;
+  [[nodiscard]] bool CreateCompatibleBitmap(const RetainPtr<CFX_DIBitmap>& pDIB,
+                                            int width,
+                                            int height) const;
   const FX_RECT& GetClipBox() const { return m_ClipBox; }
   void SetBaseClip(const FX_RECT& rect);
   bool SetClip_PathFill(const CFX_Path& path,