Fix: error reading RLE compressed Iris images

Regression in [0] which used a 4x large size bounds check
to prevent a buffer read overflow reading the RLE table.

[0]: 829916f4e5

source/blender/imbuf/intern/format_iris.cc

@@ -293,7 +293,7 @@ ImBuf *imb_loadiris(const uchar *mem, size_t size, int flags, ImFileColorSpace &
   } \
   ((void)0)
 
-    MFILE_CAPACITY_AT_PTR_OK_OR_FAIL(MFILE_DATA(inf) + ((4 * 2) * tablen));
+    MFILE_CAPACITY_AT_PTR_OK_OR_FAIL(MFILE_DATA(inf) + (2 * tablen));
 
     readtab(inf, starttab, tablen);
     readtab(inf, lengthtab, tablen);