[Media_Common][Coverity] Fix NULL_FIELD dereferences in va_trace and va_dri2

Fix two Coverity NULL_FIELD defects (CID 3528231, CID 3660939):

1. va/va_trace.c (CID 3528231): In va_TraceVPrint(), fp_log is read from
   trace_ctx->plog_file->fp_log and passed directly to vfprintf/fflush without
   a null check. Since fp_log is set from fopen() output (which can return NULL
   on failure), dereferencing it unconditionally causes undefined behavior. All
   other sites in the file that use fp_log check it for null first (lines 744,
   920, 2113, 4307). Add the missing null guard before the FILE* use.

2. va/x11/va_dri2.c (CID 3660939): VA_DRI2GetBuffers_internal() dereferences
   info->codes->major_opcode without checking info->codes for null. Both callers
   validate info->codes via XextCheckExtension/XextSimpleCheckExtension before
   calling this static helper, so this cannot be triggered in current code.
   Add a defensive early-return to make the function self-guarding and consistent
   with the pattern used in sibling functions.

Resolves: VSMGWL-85794

[Internal]
Commit_Type: Bugfix
Platforms: Gen8_12, Xe_Hpm, Xe_Lpm, Xe2_Hpm, Xe2_Lpm, Xe3_Hpm, Xe3_Lpm
OS: Linux
Feature impact: Misc
Resolves: VSMGWL-85794
Related-to: N/A

Co-Authored-By: Claude Code <noreply@anthropic.com>
diff --git a/va/va_trace.c b/va/va_trace.c
index 7ececc0..4d051ba 100644
--- a/va/va_trace.c
+++ b/va/va_trace.c
@@ -968,6 +968,8 @@
         return;
 
     fp = trace_ctx->plog_file->fp_log;
+    if (!fp)
+        return;
     if (msg)  {
         vfprintf(fp, msg, args);
     } else
diff --git a/va/x11/va_dri2.c b/va/x11/va_dri2.c
index da2a9f4..6d3637f 100644
--- a/va/x11/va_dri2.c
+++ b/va/x11/va_dri2.c
@@ -303,6 +303,9 @@
     CARD32 *p;
     int i;
 
+    if (!info->codes)
+        return NULL;
+
     GetReqExtra(DRI2GetBuffers, count * 4, req);
     req->reqType = info->codes->major_opcode;
     req->dri2ReqType = X_DRI2GetBuffers;