print.matrix incorrectly formatting string matrixes when righ (PR#3058)

When printing a string matrix with right=TRUE and na.print specified, an
incorrect amount of spaced is provided for NA columns leading to incorrect
formatting:

a <- matrix( c(NA, "a", "b", "10",

+                NA, NA,  "d", "12",
+                NA, NA,  NA,  "14"),
+              byrow=T, ncol=4 )

print(a) # correct

     [,1] [,2] [,3] [,4]
[1,] NA   "a"  "b"  "10"
[2,] NA   NA   "d"  "12"
[3,] NA   NA   NA   "14"

print(a, right=T) # correct

     [,1] [,2] [,3] [,4]
[1,]   NA  "a"  "b" "10"
[2,]   NA   NA  "d" "12"
[3,]   NA   NA   NA "14"

print(a, right=T, na.print=" ") # wrong

     [,1] [,2] [,3] [,4]
[1,]      "a"  "b" "10"
[2,]          "d" "12"
[3,]             "14"

print(a, right=T, na.print="      ") # wrong

     [,1]   [,2]   [,3]   [,4]
[1,]               "a"    "b" "10"
[2,]                          "d" "12"
[3,]                                  "14"

This does not occur with numeric matrixes:

a <- matrix( c(NA, 1.0, 2.0, 3.0,

+                NA, NA,  4.0, 5.0,
+                NA, NA,   NA, 6.0 ),

+                byrow=T, ncol=4 )

print(a)

     [,1] [,2] [,3] [,4]
[1,]   NA    1    2    3
[2,]   NA   NA    4    5
[3,]   NA   NA   NA    6

print(a,right=T)

     [,1] [,2] [,3] [,4]
[1,]   NA    1    2    3
[2,]   NA   NA    4    5
[3,]   NA   NA   NA    6

print(a,right=T,na.print=" ")

     [,1] [,2] [,3] [,4]
[1,]         1    2    3
[2,]              4    5
[3,]                   6

print(a, right=T, na.print="      ")

       [,1]   [,2]   [,3] [,4]
[1,]             1      2    3
[2,]                    4    5
[3,]                         6