Configure: don't stop everything when modplug 0.8.8 is detected, just deactivate the module

This was annoying because if you had a modplug.pc and didn't --enable-mod, it was auto-detected and then failed.
(cherry picked from commit a9d916728b2717206a0a7fe0702b0bc6dad16747)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

configure.ac

@@ -2505,15 +2505,12 @@ then
       AC_MSG_ERROR([cannot find ${real_mod_tree}/src/.libs/libmodplug.a, make sure you compiled mod in ${with_mod_tree}])
     fi
   else
-    PKG_CHECK_MODULES(LIBMODPLUG, [libmodplug >= 0.8], [
-      PKG_CHECK_MODULES(WORKING_LIBMODPLUG, [libmodplug != 0.8.8],, [
-        AC_MSG_ERROR([libmodplug version 0.8.8 will not work. Please upgrade to 0.8.8.1 or later (or downgrade to 0.8.7)!])
-      ])
-      VLC_ADD_PLUGIN([mod])
-      VLC_ADD_CXXFLAGS([mod],[$LIBMODPLUG_CFLAGS])
-      VLC_ADD_LIBS([mod],[$LIBMODPLUG_LIBS])
+    PKG_CHECK_MODULES(LIBMODPLUG, [libmodplug >= 0.8 libmodplug != 0.8.8], [
+          VLC_ADD_PLUGIN([mod])
+          VLC_ADD_CXXFLAGS([mod],[$LIBMODPLUG_CFLAGS])
+          VLC_ADD_LIBS([mod],[$LIBMODPLUG_LIBS])
     ], [
-      AC_MSG_WARN([libmodplug not found!])
+      AC_MSG_WARN([libmodplug not found or a broken version (0.8.8.0) was found!])
     ])
   fi
 fi