Fixed potential issue wehre append subroutines might fail if the appe…

…nded array has 0 size.

src/swiftest/swiftest_util.f90

@@ -31,6 +31,8 @@ module subroutine swiftest_util_append_arr_char_string(arr, source, nold, nsrc,
       if (.not. allocated(source)) return
 
       nnew = count(lsource_mask(1:nsrc))
+      if (nnew == 0) return
+
       if (.not.allocated(arr)) then
          allocate(arr(nold+nnew))
       else
@@ -59,6 +61,8 @@ module subroutine swiftest_util_append_arr_DP(arr, source, nold, nsrc, lsource_m
       if (.not. allocated(source)) return
 
       nnew = count(lsource_mask(1:nsrc))
+      if (nnew == 0) return
+
       if (.not.allocated(arr)) then
          allocate(arr(nold+nnew))
       else
@@ -87,6 +91,8 @@ module subroutine swiftest_util_append_arr_DPvec(arr, source, nold, nsrc, lsourc
       if (.not. allocated(source)) return
 
       nnew = count(lsource_mask(1:nsrc))
+      if (nnew == 0) return
+
       if (.not.allocated(arr)) then
          allocate(arr(NDIM,nold+nnew))
       else
@@ -117,6 +123,8 @@ module subroutine swiftest_util_append_arr_I4B(arr, source, nold, nsrc, lsource_
       if (.not. allocated(source)) return
 
       nnew = count(lsource_mask(1:nsrc))
+      if (nnew == 0) return
+
       if (.not.allocated(arr)) then
          allocate(arr(nold+nnew))
       else
@@ -146,6 +154,8 @@ module subroutine swiftest_util_append_arr_info(arr, source, nold, nsrc, lsource
       if (.not. allocated(source)) return
 
       nnew = count(lsource_mask(1:nsrc))
+      if (nnew == 0) return
+
       if (.not.allocated(arr)) then
          allocate(arr(nold+nnew))
       else
@@ -178,6 +188,8 @@ module subroutine swiftest_util_append_arr_kin(arr, source, nold, nsrc, lsource_
       if (.not. allocated(source)) return
 
       nnew = count(lsource_mask(1:nsrc))
+      if (nnew == 0) return
+
       if (.not.allocated(arr)) then
          allocate(arr(nold+nnew))
       else
@@ -206,6 +218,8 @@ module subroutine swiftest_util_append_arr_logical(arr, source, nold, nsrc, lsou
       if (.not. allocated(source)) return
 
       nnew = count(lsource_mask(1:nsrc))
+      if (nnew == 0) return
+
       if (.not.allocated(arr)) then
          allocate(arr(nold+nnew))
       else