add a entry to the policy about fixing warnings (i think this is common sense but if anydeveloper disagrees, just say so

and ill revert it and we can disscuss it on ffmpeg-dev)

Originally committed as revision 8410 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/ffmpeg-doc.texi

@@ -1565,6 +1565,9 @@ please use av_log() instead.
     component of the @file{libavcodec} version number appropriately. If
     it has a fourcc, add it to @file{libavformat/avienc.c}, even if it
     is only a decoder.
+@item
+    Do not change code to hide warnings without ensuring that the underlaying
+    logic is correct and thus the warning was inappropriate
 @end enumerate
 
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