It shall not be necessary for a non-resident Indian to furnish under sub-section (1) of section 139 a return of his income if—
(a) his total income in respect of which he is assessable under this Act during the previous year consisted only of investment income or income by way of long-term capital gains or both; and
(b) the tax deductible at source under the provisions of Chapter XVIIB has been deducted from such income.