security:choose_mech fix DEAD CODE warning

... by removing the "do {} while (0)" block.

Coverity CID 1306669

lib/security.c

@@ -480,56 +480,54 @@ static CURLcode choose_mech(struct connectdata *conn)
   void *tmp_allocation;
   const struct Curl_sec_client_mech *mech = &Curl_krb5_client_mech;
 
-  do {
-    tmp_allocation = realloc(conn->app_data, mech->size);
-    if(tmp_allocation == NULL) {
-      failf(data, "Failed realloc of size %u", mech->size);
-      mech = NULL;
-      return CURLE_OUT_OF_MEMORY;
-    }
-    conn->app_data = tmp_allocation;
-
-    if(mech->init) {
-      ret = mech->init(conn->app_data);
-      if(ret) {
-        infof(data, "Failed initialization for %s. Skipping it.\n",
-              mech->name);
-        continue;
-      }
+  tmp_allocation = realloc(conn->app_data, mech->size);
+  if(tmp_allocation == NULL) {
+    failf(data, "Failed realloc of size %u", mech->size);
+    mech = NULL;
+    return CURLE_OUT_OF_MEMORY;
+  }
+  conn->app_data = tmp_allocation;
+
+  if(mech->init) {
+    ret = mech->init(conn->app_data);
+    if(ret) {
+      infof(data, "Failed initialization for %s. Skipping it.\n",
+            mech->name);
+      return CURLE_FAILED_INIT;
     }
+  }
 
-    infof(data, "Trying mechanism %s...\n", mech->name);
-    ret = ftp_send_command(conn, "AUTH %s", mech->name);
-    if(ret < 0)
-      /* FIXME: This error is too generic but it is OK for now. */
-      return CURLE_COULDNT_CONNECT;
-
-    if(ret/100 != 3) {
-      switch(ret) {
-      case 504:
-        infof(data, "Mechanism %s is not supported by the server (server "
-                    "returned ftp code: 504).\n", mech->name);
-        break;
-      case 534:
-        infof(data, "Mechanism %s was rejected by the server (server returned "
-                    "ftp code: 534).\n", mech->name);
-        break;
-      default:
-        if(ret/100 == 5) {
-          infof(data, "server does not support the security extensions\n");
-          return CURLE_USE_SSL_FAILED;
-        }
-        break;
+  infof(data, "Trying mechanism %s...\n", mech->name);
+  ret = ftp_send_command(conn, "AUTH %s", mech->name);
+  if(ret < 0)
+    /* FIXME: This error is too generic but it is OK for now. */
+    return CURLE_COULDNT_CONNECT;
+
+  if(ret/100 != 3) {
+    switch(ret) {
+    case 504:
+      infof(data, "Mechanism %s is not supported by the server (server "
+            "returned ftp code: 504).\n", mech->name);
+      break;
+    case 534:
+      infof(data, "Mechanism %s was rejected by the server (server returned "
+            "ftp code: 534).\n", mech->name);
+      break;
+    default:
+      if(ret/100 == 5) {
+        infof(data, "server does not support the security extensions\n");
+        return CURLE_USE_SSL_FAILED;
       }
-      continue;
+      break;
     }
+    return CURLE_LOGIN_DENIED;
+  }
 
-    /* Authenticate */
-    ret = mech->auth(conn->app_data, conn);
+  /* Authenticate */
+  ret = mech->auth(conn->app_data, conn);
 
-    if(ret == AUTH_CONTINUE)
-      continue;
-    else if(ret != AUTH_OK) {
+  if(ret != AUTH_CONTINUE) {
+    if(ret != AUTH_OK) {
       /* Mechanism has dumped the error to stderr, don't error here. */
       return -1;
     }
@@ -545,8 +543,7 @@ static CURLcode choose_mech(struct connectdata *conn)
     /* Set the requested protection level */
     /* BLOCKING */
     (void)sec_set_protection_level(conn);
-
-  } WHILE_FALSE;
+  }
 
   return CURLE_OK;
 }