MT#57403 warning: this 'if' clause does not guard his statement..

The fix for:

     AmMimeBody.cpp: In member function 'void AmContentType::resetBoundary()':
     AmMimeBody.cpp:122:5: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
     122 |     if ((*l_it)->type == Param::BOUNDARY)
         |     ^~
     AmMimeBody.cpp:124:7: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
     124 |       params.erase(l_it);
         |       ^~~~~~

Change-Id: I96ff98ff20c83949f294fd863e5d6d3880ece9d8

core/AmMimeBody.cpp

@@ -119,9 +119,10 @@ void AmContentType::resetBoundary()
   while (it != params.end()) {
     Params::iterator l_it = it;
     it++;
-    if ((*l_it)->type == Param::BOUNDARY)
+    if ((*l_it)->type == Param::BOUNDARY) {
       delete *l_it;
       params.erase(l_it);
+    }
   }
 
   params.push_back(new Param(BOUNDARY_str, int2hex(get_random())));