Was it ever standard to pronounce "malinger" to rhyme with "ginger"?
Webster's dictionaries started including detailed pronunciation with the 1864 edition, and it looks like they always identified malinger to have a "hard g", rhyming with linger (1864, 1890, 1930). Worcester's dictionaries, however, transcribe it as having a "soft g", rhyming with ginger (1850, 1860).
Early British pronouncing dictionaries from the 18th and 19th centuries do not include the word. Daniel Jones seems to have always had it /məˈlɪŋɡə(r)/ (1913, 1917, 1944), as did Kenyon & Knott (1944).
Given the earliest record of the pronunciation of the consonants in malinger I could find was Worcester who had it rhyming with ginger, Krapp may be right in saying that that pronunciation preceded the "linger" pronunciation, but it seems to have only persisted until around the turn of the century, if not earlier.