define MAX_SIZE_BUF

esp. for asan: allocation-size-too-big
which is harmless, but throws a better error msg in add_ent_preview for a BLL.
Fixes GH #1006, fuzzing DXF input

src/common.h

@@ -61,6 +61,12 @@
 // strings also 16bits
 #define MAX_SIZE_TF 0xFFF0
 #define MAX_SIZE_T 0xFFFE
+// asan: allocation-size-too-big
+#ifdef MAX_MEM
+#define MAX_SIZE_BUF MAX_MEM
+#else
+#define MAX_SIZE_BUF UINT64_C(0x7FFFFFFFFFFFFFFF)
+#endif
 
 #if !defined AX_STRCASECMP_HEADER && !defined HAVE_STRCASECMP
 EXPORT int strcasecmp (const char *a, const char *b);

src/in_dxf.c

@@ -6935,7 +6935,7 @@ add_ent_preview (Dwg_Object *restrict obj, Bit_Chain *restrict dat,
       dxf_free_pair (pair);
       return dxf_read_pair (dat);
     }
-  if (ent->preview_size > INTMAX_MAX)
+  if (ent->preview_size >= MAX_SIZE_BUF)
     {
       LOG_ERROR ("Invalid %s.preview_size", obj->name);
       dxf_free_pair (pair);