svx: fix SID_OFFER_IMPORT and SID_ATTR_CHAR_GRABBAG having the same SID

As commit 669ad519 (colliding
SID_SVX_START based ids, 2013-06-24) suggests, new SID_SVX_START-based
SID's shouldn't be added to include/editeng/editids.hrc. However, if it
was done, at least add a comment about it to include/svx/svxids.hrc, so
it becomes obvious that the two slots have the same ID.

This makes Format -> Frame -> Area -> Bitmap have the Import Graphic
button again.

Change-Id: I2fc852200d3cc5dfbf073ed615ac83a46040e16c

include/svx/svxids.hrc

@@ -1020,9 +1020,10 @@
 
 #define SID_ATTR_BORDER_STYLES                          ( SID_SVX_START + 1140 )
 #define SID_ATTR_BORDER_DEFAULT_WIDTH                   ( SID_SVX_START + 1141 )
+// 1142 is used by editeng (SID_ATTR_CHAR_GRABBAG)
 
 //UUUU
-#define SID_OFFER_IMPORT                                ( SID_SVX_START + 1142 )
+#define SID_OFFER_IMPORT                                ( SID_SVX_START + 1143 )
 
 // IMPORTANT NOTE: adjust SID_SVX_FIRSTFREE, when adding new slot id
 #define SID_SVX_FIRSTFREE                               (SID_OFFER_IMPORT + 1)