removed sprintf usage from zstdcli.c

some static analyzers flag this standard C90 function as unsafe.

programs/zstdcli.c

@@ -1148,7 +1148,6 @@ int main(int argCount, const char* argv[])
 
             argument++;
             while (argument[0]!=0) {
-                char shortArgument[3];
 
 #ifndef ZSTD_NOCOMPRESS
                 /* compression Level */
@@ -1281,11 +1280,13 @@ int main(int argCount, const char* argv[])
 
                     /* unknown command */
                 default :
-                    sprintf(shortArgument, "-%c", argument[0]);
+                    {   char shortArgument[3] = {'-', 0, 0};
+                        shortArgument[1] = argument[0];
                         badUsage(programName, shortArgument);
                         CLEAN_RETURN(1);
                     }
                 }
+            }
             continue;
         }   /* if (argument[0]=='-') */