refactor(algorithms, graphs): empty grid check

Author: BrianLusina

algorithms/graphs/min_cost_valid_path/__init__.py

@@ -204,6 +204,8 @@ def is_valid_and_improvable(row, col) -> bool:
 
 
 def min_cost_dfs_and_bfs(grid: List[List[int]]) -> int:
+    if not grid:
+        return 0
     # Direction vectors: right, left, down, up (matching grid values 1,2,3,4)
     dirs = [(0, 1), (0, -1), (1, 0), (-1, 0)]
     num_rows = len(grid)