fix some static-analyze bugs

Author: zhangzifeng02

ijkmedia/ijkplayer/ff_ffplay.c

@@ -3898,7 +3898,7 @@ void ffp_track_statistic_l(FFPlayer *ffp, AVStream *st, PacketQueue *q, FFTrackC
         cache->packets = q->nb_packets;
     }
 
-    if (st && st->time_base.den > 0 && st->time_base.num > 0) {
+    if (q && st && st->time_base.den > 0 && st->time_base.num > 0) {
         cache->duration = q->duration * av_q2d(st->time_base) * 1000;
     }
 }

ijkmedia/ijksdl/gles2/renderer.c

@@ -144,7 +144,7 @@ IJK_GLES2_Renderer *IJK_GLES2_Renderer_create_base(const char *fragment_shader_s
 
 fail:
 
-    if (renderer->program)
+    if (renderer && renderer->program)
         IJK_GLES2_printProgramInfo(renderer->program);
 
     IJK_GLES2_Renderer_free(renderer);

ios/IJKMediaPlayer/IJKMediaPlayer/IJKMediaPlayback.m

@@ -98,7 +98,7 @@ - (void)setUrl:(NSString *)url
     if (url == _url)
         return;
 
-    if ([self.url compare:url]) {
+    if (![self.url isEqualToString:url]) {
         _urlChanged = YES;
         _url = url;
     }