[core] Fixed nonchecked empty config for packetfilter (#3031).

Author: ethouris

srtcore/common.cpp

@@ -446,6 +446,8 @@ bool SrtParseConfig(const string& s, SrtConfig& w_config)
 
     vector<string> parts;
     Split(s, ',', back_inserter(parts));
+    if (parts.empty())
+        return false;
 
     w_config.type = parts[0];
 

test/test_fec_rebuilding.cpp

@@ -222,7 +222,9 @@ TEST(TestFEC, ConfigExchange)
 
     char fec_config1 [] = "fec,cols:10,rows:10";
 
-    srt_setsockflag(sid1, SRTO_PACKETFILTER, fec_config1, (sizeof fec_config1)-1);
+    // Check empty configuration first
+    EXPECT_EQ(srt_setsockflag(sid1, SRTO_PACKETFILTER, "", 0), -1);
+    EXPECT_NE(srt_setsockflag(sid1, SRTO_PACKETFILTER, fec_config1, (sizeof fec_config1)-1), -1);
 
     EXPECT_TRUE(m1.checkApplyFilterConfig("fec,cols:10,arq:never"));