Add error messages to map and mod reading

[Sheikah45]

Fixes #2365

[codecov]

Codecov Report

Merging #2388 (9787723) into develop (1c798f0) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@              Coverage Diff              @@
##             develop    #2388      +/-   ##
=============================================
- Coverage      62.84%   62.82%   -0.02%     
  Complexity      4102     4102              
=============================================
  Files            442      442              
  Lines          18476    18478       +2     
  Branches        1128     1128              
=============================================
- Hits           11611    11609       -2     
- Misses          6241     6245       +4     
  Partials         624      624              

Impacted Files	Coverage Δ
.../com/faforever/client/map/MapUploadController.java	20.20% <0.00%> (-0.21%)	⬇️
.../com/faforever/client/mod/ModUploadController.java	66.29% <0.00%> (-0.76%)	⬇️
...main/java/com/faforever/client/map/MapService.java	80.12% <0.00%> (-0.62%)	⬇️

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