Assert CFX_AggDeviceDriver does not deal with 1 bpp bitmaps.

All the bitmaps CFX_AggDeviceDriver receives either comes from
FPDFBitmap_CreateEx() or from a function that calls
GetCreateCompatibleBitmapFormat(). Neither of those functions ever hands
out 1 bpp bitmaps. Also remove an impossible check in the same file
along the way, since the bitmap is never null.

Change-Id: I693c50905bde22174fad308a0f96cb5b2cc87ceb
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/102772
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

core/fxge/agg/fx_agg_driver.cpp

diff --git a/core/fxge/agg/fx_agg_driver.cpp b/core/fxge/agg/fx_agg_driver.cpp
index a6fcb21..7726c08 100644
--- a/core/fxge/agg/fx_agg_driver.cpp
+++ b/core/fxge/agg/fx_agg_driver.cpp
@@ -134,9 +134,6 @@
                                 const RetainPtr<CFX_DIBBase>& pSrcBitmap,
                                 int src_left,
                                 int src_top) {
-  if (!pBitmap)
-    return;
-
   int dest_left = 0;
   int dest_top = 0;
   if (!pBitmap->GetOverlapRect(dest_left, dest_top, width, height,
@@ -963,6 +960,8 @@
       m_bGroupKnockout(bGroupKnockout),
       m_pBackdropBitmap(std::move(pBackdropBitmap)) {
   DCHECK(m_pBitmap);
+  DCHECK_NE(m_pBitmap->GetFormat(), FXDIB_Format::k1bppMask);
+  DCHECK_NE(m_pBitmap->GetFormat(), FXDIB_Format::k1bppRgb);
   InitPlatform();
 }