fix corner_cases/medal_table.io and competition_tests.io

as now it is clear how the program should behave see:
https://ilias.studium.kit.edu/goto.php?target=frm_741567_102648&client_id=produktiv

src/final_assignment/task_2/tests/CornerCases.java

@@ -10,8 +10,8 @@ import org.junit.jupiter.api.Test;
  */
 public class CornerCases extends Assignment2TestBase {
     /**
-     * Tests if olympic-medal-table only lists nations which took part in some competition,
-     * but lists these which didn't win any medal
+     * Tests if olympic-medal-table lists all nations
+     * even those who didn't win any medal or didn't took part in any competition
      */
     @Test
     @DisplayName("medal-table")

src/final_assignment/task_2/tests/data/competition_tests.io

@@ -135,4 +135,7 @@ hslbxb mhzbtx
 (4,742,gzr,inmbuucrky,0,2,1,3)
 (5,537,ewo,cyvlldijdc,0,2,0,2)
 (6,719,icf,qkibhfreia,0,1,2,3)
-(7,827,mdw,iunmgurgdb,0,1,0,1)
\ No newline at end of file
+(7,827,mdw,iunmgurgdb,0,1,0,1)
+(8,319,qie,hugfleibgj,0,0,0,0)
+(9,683,zbs,boqrrcngxx,0,0,0,0)
+(10,734,mij,xkgezgcywo,0,0,0,0)

src/final_assignment/task_2/tests/data/corner_cases/medal_table.io

-Tests if olympic-medal-table only lists nations which took part in some competition,
-but lists these which didn't win any medal
+Tests if olympic-medal-table lists all nations
+even those who didn't win any medal or didn't took part in any competition
 > add-admin vorname;nachname;tester;123123123
 OK
 > login-admin tester;123123123
@@ -18,3 +18,4 @@ OK
 OK
 > olympic-medal-table
 (1,001,can,canada,0,0,0,0)
+(2,002,den,denmark,0,0,0,0)