fix relative protocol clientside for tile urls

[schloerke]

Even with the fix, this error still exists on linux in RStudio with

#now works
leaflet() %>% addTiles()

#still does not work
leaflet() %>% addProviderTiles("CartoDB.Positron")

In the inspector...

Protocol "https" is unknown 

[schloerke]

Testing Notes.

All examples should work within RStudio 1.1.x on linux except for the last one. (fails loading https)

devtools::install_github("rstudio/leaflet#526")                                                    
#> Using GitHub PAT from envvar GITHUB_PAT
#> Using GitHub PAT from envvar GITHUB_PAT
#> Downloading GitHub repo schloerke/leaflet@urlProtocol
#> from URL https://api.github.com/repos/schloerke/leaflet/zipball/urlProtocol
#> Installing leaflet
#> '/Library/Frameworks/R.framework/Resources/bin/R' --no-site-file  \
#>   --no-environ --no-save --no-restore --quiet CMD INSTALL  \
#>   '/private/var/folders/0k/bxg5lhr92sq74mb1d446ql540000gp/T/RtmprL0PE8/devtools987352a32ffb/schloerke-leaflet-1536cca'  \
#>   --library='/Users/barret/z_R_library' --install-tests
#> 
library(leaflet)                                                                                   
                                                                                                   
# should be a normal world                                                                         
leaflet() %>% addTiles()                                                                           

                                                                                                   
# should contain a map of Ames, IA with red dots / fire icons                                      
leaflet() %>% addTiles() %>% addProviderTiles("OpenFireMap") %>% setView(-93.6, 42.0285, zoom = 15)

                                                                                                   
# should contain a map of the USA with blue heatmap-like lines/dots over highway areas             
leaflet() %>% addTiles() %>% addProviderTiles("SafeCast") %>% setView(-97, 38, zoom = 5)           

                                                                                                   
# should contain a greyscale map of the world. Fails on linux & RStudio combo                      
leaflet() %>% addProviderTiles("CartoDB.Positron")                                                 

[tim-salabim]

On my linux machine in RStudio viewer:

1. works fine
2. works fine
3. crashes RStudio completely
4. doesn't show any map

[jcheng5]

@tim-salabim The crash for 3 is a little scary. 4 is expected.

The situation is not ideal, but I'm guessing this is the best we'll be able to do. For what it's worth, all of these should work perfectly in RStudio 1.2 on all platforms.

[tim-salabim]

Is it worth testing with a daily RStudio build? If so, I will do so tonite

[tim-salabim]

With RStudio version 1.2.567 all 4 examples work as expected, no crashing, no blank viewer panes