convert(x, to = "stm") fails when dfm is 0% sparse #701

convert(as.dfm(matrix(c(1, 2, 3, 4, 5, 6, 7, 8, 0), ncol = 3)), to = "stm")
# $documents
# $documents$doc1
# [,1] [,2] [,3]
# [1,]    1    2    3
# [2,]    1    4    7
# 
# $documents$doc2
# [,1] [,2] [,3]
# [1,]    1    2    3
# [2,]    2    5    8
# 
# $documents$doc3
# [,1] [,2]
# [1,]    1    2
# [2,]    3    6
# 
# 
# $vocab
# [1] "feat1" "feat2" "feat3"
# 
# $meta
# NULL

convert(as.dfm(matrix(c(1, 2, 3, 4, 5, 6, 7, 8, 9), ncol = 3)), to = "stm")
# $documents
# 1 2 3
# [1,] 1 1 1
# [2,] 1 2 3
# [3,] 2 2 2
# [4,] 4 5 6
# [5,] 3 3 3
# [6,] 7 8 9
# attr(,"names")
# [1] "doc1" "doc2" "doc3" NA     NA     NA     NA     NA     NA     NA     NA     NA     NA    
# [14] NA     NA     NA     NA     NA    
# 
# $vocab
# [1] "feat1" "feat2" "feat3"
# 
# $meta
# NULL