core: fix buffer overflow in function eval_string_base_encode

ChangeLog.adoc

@@ -20,6 +20,7 @@ https://weechat.org/files/releasenotes/ReleaseNotes-devel.html[release notes]
 
 Bug fixes::
 
+  * core: fix buffer overflow in function eval_string_base_encode
   * core: fix integer overflow in function util_version_number
   * core: fix integer overflow in base32 encoding/decoding
   * core: fix integer overflow with decimal numbers in calculation of expression

src/core/wee-eval.c

@@ -906,7 +906,7 @@ eval_string_base_encode (const char *text)
 
     ptr_string++;
     length = strlen (ptr_string);
-    result = malloc ((length * 4) + 1);
+    result = malloc ((length * 4) + 8 + 1);
     if (!result)
         goto end;