Fix GH-2201: Drop imagesx() return false description

As of PHP 8.0.0, GD images are objects, while previously they have been
resources.  If incompatible objects are passed to respective GD
functions, that throws a `TypeError` which does not have to be
documented explicitly.  If invalid resources have been passed, that
emitted `E_WARNING` and the functions returned `false`.  In a perfect
world, we would document that for each function, but to be brief, we
just augment the respective language-snippet to express that valid `gd`
resources have been expected.  Readers should be able to figure out the
detailed behavior (and would want to avoid passing invalid resources
anyway).

Author: cmb69

language-snippets.ent

@@ -962,7 +962,7 @@ purposes.</simpara></warning>'>
  <entry>8.0.0</entry>
  <entry>
   <parameter>image</parameter> expects a <classname>GdImage</classname>
-  instance now; previously, a <type>resource</type> was expected.
+  instance now; previously, a valid <literal>gd</literal> <type>resource</type> was expected.
  </entry>
 </row>'>
 

reference/image/functions/imagesx.xml

@@ -26,8 +26,7 @@
  <refsect1 role="returnvalues">
   &reftitle.returnvalues;
   <para>
-   Return the width of the <parameter>image</parameter> or &false; on 
-   errors.
+   Return the width of the <parameter>image</parameter>.
   </para>
  </refsect1>