shared/bap: Fix not reading all instances of PAC Sinks/Sources

Both PAC Sink and Source are allowed to have multiple instances:

 - The server wanted to support a smaller maximum transmission unit
 (ATT_MTU, as defined in Volume 3, Part F, Section 3.2.8 in [2]) size.
 Exposing all supported PAC records in a single Sink PAC characteristic
 would require the server to increase its supported Maximum
 Transmission Unit (MTU) size to a value the server considered
 excessive.
 - The server wanted to expose support for proprietary audio
 capabilities (such as vendor-specific audio codecs, as denoted by the
 Codec_ID parameter value) separately from support for
 non-vendor-specific audio capabilities and used separate Sink PAC
 characteristics to expose such support.
 - The server wanted to minimize the amount of data to be transferred,
 when sending notifications to a client that the Sink PAC
 characteristic value changed, by exposing the audio capabilities
 likely to change quicker than others in separate Sink PAC
 characteristics.

src/shared/bap.c

@@ -2908,21 +2908,25 @@ static void foreach_pacs_char(struct gatt_db_attribute *attr, void *user_data)
 		DBG(bap, "Sink PAC found: handle 0x%04x", value_handle);
 
 		pacs = bap_get_pacs(bap);
-		if (!pacs || pacs->sink)
+		if (!pacs)
 			return;
 
-		pacs->sink = attr;
+		if (!pacs->sink)
+			pacs->sink = attr;
+
 		bap_read_value(bap, value_handle, read_sink_pac, bap);
 	}
 
 	if (!bt_uuid_cmp(&uuid, &uuid_source)) {
 		DBG(bap, "Source PAC found: handle 0x%04x", value_handle);
 
 		pacs = bap_get_pacs(bap);
-		if (!pacs || pacs->source)
+		if (!pacs)
 			return;
 
-		pacs->source = attr;
+		if (!pacs->source)
+			pacs->source = attr;
+
 		bap_read_value(bap, value_handle, read_source_pac, NULL);
 	}