ProfileInfo API may create extraneous base profile when updating credentials

[t1m0thyj]

Actual Behavior
When ProfileInfo.updateProperty is used to update user & password in a nested profile inside Project Config, an unexpected base profile may be created.

Expected Behavior
The ProfileInfo API should not create a new profile when asked to update properties inside an existing profile.

Steps to Reproduce

1. Create a Global Config with flat structure that includes base profile (e.g. result of zowe config init)
2. Create a Project Config with nested zosmf profile (e.g. lpar1.zosmf) and w/o base profile
3. Use the ProfileInfo API to update user & password in the nested zosmf profile:

   const { ProfileInfo } = require("@zowe/imperative");
   (async () => {
       const profInfo = new ProfileInfo("zowe");
       await profInfo.readProfilesFromDisk();
       const upd = { profileName: "lpar1.zosmf", profileType: "zosmf" };
       await profInfo.updateProperty({ ...upd, property: "user", value: "abc", setSecure: true });
       await profInfo.updateProperty({ ...upd, property: "password", value: "def", setSecure: true });
   })();

4. Notice that a new base profile gets created in Project Config which contains only a user property:

   "base": {
     "properties": {},
     "secure": [
       "user"
     ]
   }

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