how to append column to dataframe conditionally in r

I'm reading a csv file which contains coordinates of destination and origin and calculating the distance between origin and destination.

I want to check if any of the cordinates are blank or zero then skip that row and append "0" in another column else the calculated distance, here is the code

library(XML)
library(RCurl)

latlon2ft <- function(origin,destination){
  xml.url <- paste0('http://ift.tt/19WUt3A',origin,'&destinations=',destination,'&mode=driving&sensor=false')
  xmlfile <- xmlParse(getURL(xml.url))
  dist <- xmlValue(xmlChildren(xpathApply(xmlfile,"//distance")[[1]])$value)
  distance <- as.numeric(sub(" km","",dist))
  ft <- distance/1000 
  return(ft)
}
ahg = list()
for(i in 1:dim(df2)[1]){
  print(i)
  if(df2[i,4] || df2[i,5] || df2[i,2] || df2[i,3] == 0) {
  df2$Dist = "0"} else {
  ahg[[i]] = latlon2ft(origin=paste(as.character(df2[i,4:5]),collapse = ","),destination= paste(as.character(df2[i,2:3]),collapse = ","))
  df2$Dist = ahg[[i]]
  }
}

but for this code the O/P of newly calculated column Dist always gives "0". What m I missing in the code.any help would be appreciated.

Thanks. Here is sample dataframe

dput(head(df2,5))
structure(list(PROJECT_ID = c(29003L, 16717L, 6807L, 18993L, 
16099L), PXVAL = c(0.0000, 18.5504, 18.56816491, 18.7580765, 
18.5921), PYVAL = c(0.0000, 73.9412, 73.7800169, 73.6109224, 
73.7738), LAT = c(18.529349, 18.529349, 18.529349, 18.529349, 
18.529349), LNG = c(73.852879, 73.852879, 73.852879, 73.852879, 
73.852879), Dist = c("0", "0", "0", "0", "0")), .Names = c("PROJECT_ID", 
"PXVAL", "PYVAL", "LAT", "LNG", "Dist"), spec = structure(list(
    cols = structure(list(PROJECT_ID = structure(list(), class = c("collector_integer", 
    "collector")), PXVAL = structure(list(), class = c("collector_double", 
    "collector")), PYVAL = structure(list(), class = c("collector_double", 
    "collector")), LAT = structure(list(), class = c("collector_double", 
    "collector")), LNG = structure(list(), class = c("collector_double", 
    "collector"))), .Names = c("PROJECT_ID", "PXVAL", "PYVAL", 
    "LAT", "LNG")), default = structure(list(), class = c("collector_guess", 
    "collector"))), .Names = c("cols", "default"), class = "col_spec"), row.names = c(NA, 
5L), class = c("tbl_df", "tbl", "data.frame"))

Expected O/P

ID    PXVAL        PYVAL           LAT      LNG         Dist
29003   0.0000        0        18.529349    73.852879   0
16717   18.5504     73.9412    18.529349    73.852879   12.3
6807    18.56816491 73.7800169  18.529349   73.852879   20.5
18993   18.7580765  73.6109224  18.529349   73.852879   8.10
16099   18.5921      73.7738    18.529349   73.852879   45.2