Vulkan: fixes driver name concatenation on multi-GPU systems (#2620)

* Vulkan: fixes driver name concatenation on multi-GPU systems

applyDriverName appended to the result buffer without clearing it. When
a later device reported a higher API version, its driver name was
appended to the name of the earlier device instead of replacing it, as
the comment in detectVulkan intends.

* CHANGELOG: moves the #2615 entry to Unreleased

#2616 was opened after 2.69.0 had been released, but its entry was
written under 2.69.0 Bugfixes, so the changelog listed the fix as part
of 2.69.0.

src/detection/vulkan/vulkan.c

@@ -19,6 +19,8 @@ static inline void applyVulkanVersion(uint32_t vulkanVersion, FFVersion* ffVersi
 }
 
 static void applyDriverName(VkPhysicalDeviceDriverPropertiesKHR* properties, FFstrbuf* result) {
+    ffStrbufClear(result);
+
     if (!ffStrSet(properties->driverName)) {
         return;
     }