don't free "static" alpha data (patch 1738966) [backport from HEAD]

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@46549 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -99,6 +99,7 @@ All (GUI):
   enough to select half of a character (Michael Hieke)
 - Significantly improved startup times of XRC-based applications using
   embedded resources on Unix (requires resources recompilation)
+- Fixed freeing of "static" alpha data in wxImage (Axel Gembe)
 
 wxMSW:
 

src/common/image.cpp

@@ -1671,7 +1671,9 @@ void wxImage::SetAlpha( unsigned char *alpha, bool static_data )
         alpha = (unsigned char *)malloc(M_IMGDATA->m_width*M_IMGDATA->m_height);
     }
 
-    free(M_IMGDATA->m_alpha);
+    if( !M_IMGDATA->m_staticAlpha )
+        free(M_IMGDATA->m_alpha);
+
     M_IMGDATA->m_alpha = alpha;
     M_IMGDATA->m_staticAlpha = static_data;
 }
@@ -1904,8 +1906,11 @@ bool wxImage::ConvertAlphaToMask(unsigned char threshold)
         }
     }
 
-    free(M_IMGDATA->m_alpha);
+    if( !M_IMGDATA->m_staticAlpha )
+        free(M_IMGDATA->m_alpha);
+
     M_IMGDATA->m_alpha = NULL;
+    M_IMGDATA->m_staticAlpha = false;
 
     return true;
 }