b/f: fix false positive matching keys with prefixes in get_header_keyvalue

e.g. P-App-Param: prefixmykey=myprefixval;mykey=myval would not work with
mykey.

int bug #59

core/AmUtils.cpp

@@ -819,6 +819,8 @@ string get_header_keyvalue_single(const string& param_hdr, const string& name) {
 	    st = ST_CMPKEY;
 	  k_begin = p;
 	  corr = 1;
+	} else {
+	  st = ST_FINDBGN;
 	}
       }
     } break;

core/tests/test_headers.cpp

@@ -34,8 +34,8 @@ FCTMF_SUITE_BGN(test_headers) {
     } FCT_TEST_END();
 
     FCT_TEST_BGN(getHeader_keyvalue) {
-      fct_chk(get_header_keyvalue("mykey=myval;myotherkey=myval", "mykey") == "myval");
-      fct_chk(get_header_keyvalue("mykey=myval;myotherkey=myval", "myotherkey") == "myval");
+      fct_chk(get_header_keyvalue("mykey=myval;myotherkey=myotherval", "mykey") == "myval");
+      fct_chk(get_header_keyvalue("mykey=myval1;myotherkey=myval", "myotherkey") == "myval");
       fct_chk(get_header_keyvalue("mykey=myval;myotherkey=", "myotherkey") == "");
       fct_chk(get_header_keyvalue(getHeader("P-My-Test: mykey=myval;myotherfunkykey=myval" CRLF, "P-My-Test", true), "mykey") == "myval" );
 
@@ -57,7 +57,13 @@ FCTMF_SUITE_BGN(test_headers) {
       fct_chk(get_header_keyvalue(getHeader("P-My-Test: mykey=myval; myotherfunkykey= 'test \\' escaped';andsomemore", "P-My-Test", true), "test \\' escaped") == "");
       fct_chk(get_header_keyvalue("u=sayer;d=iptel.org;p=abcdef", "u") == "sayer");
       fct_chk(get_header_keyvalue("u=sayer;d=iptel.org;p=abcdef", "d") == "iptel.org");
-    } FCT_TEST_END();
+
+      fct_chk(get_header_keyvalue("prefixmykey=myprefixval;mykey=myval", "mykey") == "myval");
+      fct_chk(get_header_keyvalue("some=other;prefixmykey=myprefixval;mykey=myval", "mykey") == "myval");
+      fct_chk(get_header_keyvalue("some=\"mykey\";prefixmykey=myprefixval;mykey=myval", "mykey") == "myval");
+      fct_chk(get_header_keyvalue("some=\"mykey=valx\";prefixmykey=myprefixval;mykey=myval", "mykey") == "myval");
+
+   } FCT_TEST_END();
 
 
     FCT_TEST_BGN(getHeader_allow) {