Deallocate observation index arrays before re-allocation

[jjokella]

Otherwise Segmentation a segmentation fault is happening, when observation sizes (dim_obs) vary (in particular a larger dim_obs after a smaller one).

[jwc01n074:604206:0:604206] Caught signal 11 (Segmentation fault: address not mapped to object at address 0x145d273c5000)
[jwc01n075:610522:0:610522] Caught signal 11 (Segmentation fault: address not mapped to object at address 0x154343e9d000)
[jwc01n073:532909:0:532909] Caught signal 11 (Segmentation fault: address not mapped to object at address 0x15360d613000)
==== backtrace (tid: 604206) ====
 0 0x000000000003e730 __GI___sigaction()  :0
 1 0x0000000000611691 enkf_clm_mod_mp_domain_def_clm_()  ./pdaf/interface/model/eclm/enkf_clm_mod_5.F90:1052
 2 0x0000000000440bdf init_dim_obs_f_pdaf_()  ./pdaf/interface/framework/init_dim_obs_f_pdaf.F90:402
 3 0x000000000059d875 pdaf_lestkf_update_()  ./pdaf/src/PDAF_lestkf_update.F90:280
 4 0x000000000059b5a0 pdaf_lestkf_update_.t431p.t432p.t433p.t434p.t435p.t436p.t437p.t438p.t439p.t440p.t441p.t442p.t443p.t444p.t445p.t446p.t447p.t448p.t449p.t450p.t451p.t452p.t453p.t454p.t455p.t456p.t457p.t458p.t459p.t460p.t461p.t462p()  ./pdaf/src/PDAF_put_state_lestkf.F90:0
 5 0x000000000059b30d pdaf_put_state_lestkf_()  ./pdaf/src/PDAF_put_state_lestkf.F90:189
 6 0x00000000004ba431 pdaf_put_state_lestkf_.t211p.t212p.t213p.t214p.t215p.t216p.t217p.t218p.t219p.t220p.t221p.t222p.t223p.t224p.t225p.t226p()  ./pdaf/src/PDAF_assimilate_lestkf.F90:0
 7 0x00000000004ba2e4 pdaf_assimilate_lestkf_()  ./pdaf/src/PDAF_assimilate_lestkf.F90:124
 8 0x000000000042a876 pdaf_assimilate_lestkf_.t310p.t311p.t312p.t313p.t314p.t315p.t316p.t317p.t318p.t319p.t320p.t321p.t322p.t323p.t324p.t325p.t326p.t327p()  ./pdaf/interface/framework/assimilate_pdaf.F90:0
 9 0x000000000042a193 assimilate_pdaf_()  ./pdaf/interface/framework/assimilate_pdaf.F90:147
10 0x000000000042050b assimilate_pdaf_.void()  ./pdaf/interface/framework/pdaf_terrsysmp.F90:0
11 0x0000000000420489 MAIN__()  ./pdaf/interface/framework/pdaf_terrsysmp.F90:92
12 0x0000000000418d0d main()  ???:0
13 0x00000000000295d0 __libc_start_call_main()  ???:0
14 0x0000000000029680 __libc_start_main_alias_2()  :0
15 0x0000000000418c25 _start()  ???:0