MT#59962 AmSdp: `parse_sdp_attr()` initialize integers

Before using the `clock_rate` or `payload_type`
always initialize, because might be used non-defined,
which will give whatever value.

Fixes:

    Uninitialized scalar variable (UNINIT)
    35. uninit_use_in_call: Using uninitialized
        value (int)clock_rate when calling SdpPayload.

Change-Id: Ie7cea4289ace93a169ad2dce8a402b9a469c65f8

core/AmSdp.cpp

@@ -1046,7 +1046,7 @@ static char* parse_sdp_attr(AmSdp* sdp_msg, char* s)
   int parsing = 1;
   line_end = skip_till_next_line(attr_line, line_len);
 
-  unsigned int payload_type, clock_rate, encoding_param = 0;
+  unsigned int payload_type = 0, clock_rate = 0, encoding_param = 0;
   string encoding_name, params;
 
   string attr;