Need better handling of GUROBI solver error

[klin333]

Describe the bug
Trycatch of solver error for GUROBI is not done well, resulting is cryptic error message shown to users of CVXR when the solver fails.

To Reproduce

library(CVXR)

x <- Variable(1)
d <- NA_real_

prob <- Problem(Minimize(x/d), list(x >= 0))
res <- solve(prob, solver = 'GUROBI')

Expected behavior
We expect a SOLVER_ERROR status. Note that running gurobi::gurobi directly on the model will show an error message of "Error: model$obj contains NA". However for CVXR, simple indication of SOLVER_ERROR is fine.

Output
Error in if (status == 2 || status == "OPTIMAL") OPTIMAL else if (status == :
missing value where TRUE/FALSE needed

Version
R version 3.6.3 (2020-02-29)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 19043)

Matrix products: default

locale:
[1] LC_COLLATE=English_Australia.1252 LC_CTYPE=English_Australia.1252 LC_MONETARY=English_Australia.1252
[4] LC_NUMERIC=C LC_TIME=English_Australia.1252

attached base packages:
[1] graphics grDevices utils methods base

other attached packages:
[1] CVXR_1.0-9

loaded via a namespace (and not attached):
[1] Rcpp_1.0.4.6 gurobi_9.5-0 lattice_0.20-38 packrat_0.5.0 gmp_0.6-2 slam_0.1-48
[7] grid_3.6.3 R6_2.4.1 modules_0.8.0 Rmpfr_0.8-1 renv_0.13.2 Matrix_1.2-18
[13] tools_3.6.3 bit64_0.9-7 glue_1.4.1 bit_1.1-15.2 rsconnect_0.8.16 compiler_3.6.3
[19] stats_3.6.3 BiocManager_1.30.10

Additional context

The problem is likely due to qp_solvers.R, in the setMethod("solve_via_data", "GUROBI_QP").

results_dict <- list()
  tryCatch({
    results_dict$solution <- gurobi::gurobi(model, params)   # Solve.
  }, error = function(e) {   # Error in the solution.
    results_dict$status <- 'SOLVER_ERROR'
  })

When solver fails, $solution is NULL. However, in setMethod("invert", signature(object = "GUROBI_QP",..), it tries to do status_map(object, solution$status), causing the above cryptic error message.

Same thing with conic_solvers.R

Maybe change it to results_dict$solution$status <- 'SOLVER_ERROR'