Force textarea of text and richtext to inherit minimal height

issue8656
review288051003

src/sao.less

@@ -450,6 +450,11 @@ img.icon {
             max-height: 300px;
         }
     }
+    .form-text, .form-richtext {
+        > textarea {
+            min-height: inherit;
+        }
+    }
     .form-richtext {
         > .btn-toolbar {
             min-width: 450px;