fix(command_line): handle missing flags

This commit fixes the command_line_t flag_value type-bound
procedure to allocate and return a string of zero length when a
flag is not found. Previously, the procdure would return an
unallocated string, which caused test crashes.

Author: rouson

src/sourcery/sourcery_command_line_s.f90

@@ -39,23 +39,28 @@
     integer argnum, arglen, flag_value_length
     character(len=:), allocatable :: arg
 
-
-    flag_search: &
-    do argnum = 1,command_argument_count()
-
-      if (allocated(arg)) deallocate(arg)
-
-      call get_command_argument(argnum, length=arglen)
-      allocate(character(len=arglen) :: arg)
-      call get_command_argument(argnum, arg)
-
-      if (arg==flag) then
-        call get_command_argument(argnum+1, length=flag_value_length)
-        allocate(character(len=flag_value_length) :: flag_value)
-        call get_command_argument(argnum+1, flag_value)
-        exit flag_search
+    associate(argcount => command_argument_count())
+      if (argcount==0) then
+        flag_value=""
+      else
+        flag_search: &
+        do argnum = 1,argcount
+
+          if (allocated(arg)) deallocate(arg)
+
+          call get_command_argument(argnum, length=arglen)
+          allocate(character(len=arglen) :: arg)
+          call get_command_argument(argnum, arg)
+
+          if (arg==flag) then
+            call get_command_argument(argnum+1, length=flag_value_length)
+            allocate(character(len=flag_value_length) :: flag_value)
+            call get_command_argument(argnum+1, flag_value)
+            exit flag_search
+          end if
+        end do flag_search
       end if
-    end do flag_search
+    end associate
 
   end procedure