filter/chain: copy the child name

filter_chain_parse() passes a temporary string pointer which results
in a use-after-free in the PreparedChainFilter::Child::Open() error
message.

NEWS

@@ -1,6 +1,8 @@
 ver 0.22.3 (not yet released)
 * playlist
   - add option "as_directory", making CUE file expansion optional
+* filter
+  - fix garbage after "Audio format not supported by filter" message
 
 ver 0.22.2 (2020/10/28)
 * database

src/filter/plugins/ChainFilterPlugin.cxx

@@ -28,6 +28,7 @@
 #include <cassert>
 #include <list>
 #include <memory>
+#include <string>
 
 class ChainFilter final : public Filter {
 	struct Child {
@@ -72,7 +73,7 @@ private:
 
 class PreparedChainFilter final : public PreparedFilter {
 	struct Child {
-		const char *name;
+		const std::string name;
 		std::unique_ptr<PreparedFilter> filter;
 
 		Child(const char *_name,
@@ -105,7 +106,7 @@ PreparedChainFilter::Child::Open(const AudioFormat &prev_audio_format)
 
 	if (conv_audio_format != prev_audio_format)
 		throw FormatRuntimeError("Audio format not supported by filter '%s': %s",
-					 name,
+					 name.c_str(),
 					 ToString(prev_audio_format).c_str());
 
 	return new_filter;