*: let libfmt quote strings

src/mixer/All.cxx

@@ -33,7 +33,7 @@ output_mixer_get_volume(const AudioOutputControl &ao) noexcept
 		return mixer->LockGetVolume();
 	} catch (...) {
 		FmtError(mixer_domain,
-			 "Failed to read mixer for '{}': {}",
+			 "Failed to read mixer for {:?}: {}",
 			 ao.GetName(), std::current_exception());
 		return -1;
 	}
@@ -88,9 +88,9 @@ output_mixer_set_volume(AudioOutputControl &ao, unsigned volume)
 		return SetVolumeResult::OK;
 	} catch (...) {
 		FmtError(mixer_domain,
-			 "Failed to set mixer for '{}': {}",
+			 "Failed to set mixer for {:?}: {}",
 			 ao.GetName(), std::current_exception());
-		std::throw_with_nested(std::runtime_error(FmtBuffer<256>("Failed to set mixer for '{}'",
+		std::throw_with_nested(std::runtime_error(FmtBuffer<256>("Failed to set mixer for {:?}",
 									 ao.GetName())));
 	}
 }

src/mixer/plugins/OssMixerPlugin.cxx

@@ -108,7 +108,7 @@ OssMixer::Open()
 				throw MakeErrno("READ_DEVMASK failed");
 
 			if (((1 << volume_control) & devmask) == 0)
-				throw FmtErrno("mixer control \"{}\" not usable",
+				throw FmtErrno("mixer control {:?} not usable",
 					       control);
 		}
 	} catch (...) {
@@ -134,8 +134,8 @@ OssMixer::GetVolume()
 
 	if (left != right) {
 		FmtWarning(oss_mixer_domain,
-			   "volume for left and right is not the same, \"{}\" and "
-			   "\"{}\"\n", left, right);
+			   "volume for left and right is not the same, {:?} and "
+			   "{:?}\n", left, right);
 	}
 
 	return left;

src/mixer/plugins/PulseMixerPlugin.cxx

@@ -161,7 +161,7 @@ parse_volume_scale_factor(const char *value) {
 	float factor = ParseFloat(value, &endptr);
 
 	if (endptr == value || *endptr != '\0' || factor < 0.5f || factor > 5.0f)
-		throw FmtRuntimeError("\"{}\" is not a number in the "
+		throw FmtRuntimeError("{:?} is not a number in the "
 				      "range 0.5 to 5.0",
 				      value);