[NI] Remove lambda coersion to Unit in case of error return type(s)

Coersion to Unit from error type leads to misleading type mismatches:
"expected <expected lambda return type> found Unit", despite no user-provided Unit / empty lambda.
These diagnostics were collected, but not reported before, and that had been disguising the issue for a while.

KT-34729 Fixed

compiler/testData/diagnostics/tests/resolve/newLineLambda.kt

@@ -104,9 +104,9 @@ fun testTwoLambdas() {
             <!OI;TYPE_MISMATCH!>twoLambdaArgs({})
             {}
             <!MANY_LAMBDA_EXPRESSION_ARGUMENTS, UNEXPECTED_TRAILING_LAMBDA_ON_A_NEW_LINE!>{}<!><!>
-        } else {
+        } else <!NI;TYPE_MISMATCH!>{
             {}
-        }<!>
+        }<!><!>
     }
 }