contrib: soxr: expand internal Real Discrete Fourier Transform buffers

With FFmpeg 6.1 an extra item in the buffer is needed.
The API was introduced in af94ab7c7c
But it was only made the default in 6.1 since 83ede01bb0

This results in an out of bounds writing error on Windows.

contrib/src/soxr/0001-Allocate-an-extra-real-number.patch

@@ -0,0 +1,41 @@
+From adcb67039236cb7a67e91c897372332f25a7cfa4 Mon Sep 17 00:00:00 2001
+From: Steve Lhomme <robux4@ycbcr.xyz>
+Date: Mon, 25 Mar 2024 10:29:19 +0100
+Subject: [PATCH] Allocate an extra real number
+
+In newer libavutil the FFT buffer needs room for an extra value.
+
+The algorithm writes at len2 index which corresponds to our dft_length length:
+https://github.com/FFmpeg/FFmpeg/commit/af94ab7c7c004786084903bcf82b7617e88e3aa9
+---
+ src/cr.c | 6 +++---
+ 1 file changed, 3 insertions(+), 3 deletions(-)
+
+diff --git a/src/cr.c b/src/cr.c
+index 4122db3..e765829 100644
+--- a/src/cr.c
++++ b/src/cr.c
+@@ -201,7 +201,7 @@ static void dft_stage_init(
+     else f->post_peak = num_taps / 2;
+ 
+     dft_length = set_dft_length(num_taps, (int)min_dft_size, (int)large_dft_size);
+-    f->coefs = rdft_calloc((size_t)dft_length, sizeof_real);
++    f->coefs = rdft_calloc((size_t)dft_length+1, sizeof_real);
+     offset = dft_length - num_taps + 1;
+     m = (1. / dft_length) * rdft_multiplier() * L * *multiplier;
+     if (IS_FLOAT32) for (i = 0; i < num_taps; ++i)
+@@ -212,9 +212,9 @@ static void dft_stage_init(
+   }
+ 
+   if (rdft_flags() & RDFT_IS_SIMD)
+-    p->dft_out = rdft_malloc(sizeof_real * (size_t)dft_length);
++    p->dft_out = rdft_malloc(sizeof_real * (size_t)(dft_length+1));
+   if (rdft_flags() & RDFT_NEEDS_SCRATCH)
+-    p->dft_scratch = rdft_malloc(2 * sizeof_real * (size_t)dft_length);
++    p->dft_scratch = rdft_malloc(2 * sizeof_real * (size_t)(dft_length+1));
+ 
+   if (!f->dft_length) {
+     void * coef_setup = rdft_forward_setup(dft_length);
+-- 
+2.37.3.windows.1
+

contrib/src/soxr/rules.mak

@@ -23,6 +23,7 @@ soxr: soxr-$(SOXR_VERSION)-Source.tar.xz .sum-soxr
 	$(APPLY) $(SRC)/soxr/find_ff_pkgconfig.patch
 	$(APPLY) $(SRC)/soxr/soxr-check-function.patch
 	$(APPLY) $(SRC)/soxr/aarch64.patch
+	$(APPLY) $(SRC)/soxr/0001-Allocate-an-extra-real-number.patch
 	$(call pkg_static,"src/soxr.pc.in")
 	$(MOVE)