Fix four annoying warnings:

core/src/fpdfapi/fpdf_edit/fpdf_edit_image.cpp

Index: core/src/fpdfapi/fpdf_edit/fpdf_edit_image.cpp
diff --git a/core/src/fpdfapi/fpdf_edit/fpdf_edit_image.cpp b/core/src/fpdfapi/fpdf_edit/fpdf_edit_image.cpp
index a5a91ebc53ba719e09d0a6705c601a5aa9acfced..bb80196d6f6a15015f1eadb35f59da560b2dbfb5 100644
--- a/core/src/fpdfapi/fpdf_edit/fpdf_edit_image.cpp
+++ b/core/src/fpdfapi/fpdf_edit/fpdf_edit_image.cpp
@@ -190,8 +190,10 @@ void CPDF_Image::SetImage(const CFX_DIBitmap* pBitmap, FX_INT32 iCompress, IFX_F
         }
     }
     const CFX_DIBitmap* pMaskBitmap = NULL;
+    FX_BOOL bDeleteMask = FALSE;
     if (pBitmap->HasAlpha()) {
         pMaskBitmap = pBitmap->GetAlphaMask();
+        bDeleteMask = TRUE;
     }
     if (!pMaskBitmap && pMask) {
         FXDIB_Format maskFormat = pMask->GetFormat();
@@ -204,7 +206,6 @@ void CPDF_Image::SetImage(const CFX_DIBitmap* pBitmap, FX_INT32 iCompress, IFX_F
         FX_INT32 maskHeight = pMaskBitmap->GetHeight();
         FX_LPBYTE mask_buf = NULL;
         FX_STRSIZE mask_size;
-        FX_BOOL bDeleteMask = TRUE;
         CPDF_Dictionary* pMaskDict = new CPDF_Dictionary;
         pMaskDict->SetAtName(FX_BSTRC("Type"), FX_BSTRC("XObject"));
         pMaskDict->SetAtName(FX_BSTRC("Subtype"), FX_BSTRC("Image"));
@@ -240,7 +241,7 @@ void CPDF_Image::SetImage(const CFX_DIBitmap* pBitmap, FX_INT32 iCompress, IFX_F
             bDeleteMask = FALSE;
             pDict->SetAtReference(FX_BSTRC("SMask"), m_pDocument, pMaskStream);
         }
-        if (pBitmap->HasAlpha()) {
+        if (bDeleteMask) {
             delete pMaskBitmap;
         }
     }