libtheora: fetch a patch instead of storing it in Spack (#20620)

var/spack/repos/builtin/packages/libtheora/dont_use_png_sizeof.patch

@@ -1,19 +0,0 @@
-diff --git a/examples/png2theora.c b/examples/png2theora.c
-index 71a0d0f..ed24c2a 100644
---- a/examples/png2theora.c
-+++ b/examples/png2theora.c
-@@ -462,9 +462,9 @@ png_read(const char *pathname, unsigned int *w, unsigned int *h, unsigned char *
-   png_set_strip_alpha(png_ptr);
- 
-   row_data = (png_bytep)png_malloc(png_ptr,
--    3*height*width*png_sizeof(*row_data));
-+    3*height*width*sizeof(*row_data));
-   row_pointers = (png_bytep *)png_malloc(png_ptr,
--    height*png_sizeof(*row_pointers));
-+    height*sizeof(*row_pointers));
-   for(y = 0; y < height; y++) {
-     row_pointers[y] = row_data + y*(3*width);
-   }
--- 
-2.7.4
-

var/spack/repos/builtin/packages/libtheora/package.py

@@ -21,9 +21,11 @@ class Libtheora(AutotoolsPackage):
     depends_on('m4',       type='build')
     depends_on('doxygen',  type='build')
     depends_on('libogg')
+    depends_on('libpng')
 
     patch('exit-prior-to-running-configure.patch', when='@1.1.1')
-    patch('dont_use_png_sizeof.patch', when='@1.1.1')
+    patch('https://gitlab.xiph.org/xiph/theora/-/commit/7288b539c52e99168488dc3a343845c9365617c8.patch',
+          sha256='2e4f891f6880386d9391f3e4eaf4a23493de4eea532f9b5cb8a04b5f7cd09301', when='^libpng@1.6:')
 
     def autoreconf(self, spec, prefix):
         sh = which('sh')