Improve robustness

nx is 0 if the script is run on a triplet of shapefiles for
interpolated eddies.

Analysis/distribution_function.py

@@ -10,10 +10,13 @@ def plot_distr_funct(x, label = None, ax = None):
     
     x.sort()
     nx = np.size(x)
-    if ax is None: ax = plt.gca()
-    ax.plot(x, (1 + np.arange(nx)) / nx, label = label)
-    print("minimum value:", x[0])
-    print("maximum value:", x[-1])
+    
+    if nx != 0:
+        if ax is None: ax = plt.gca()
+        ax.plot(x, (1 + np.arange(nx)) / nx, label = label)
+        print("minimum value:", x[0])
+        print("maximum value:", x[-1])
+        
     print("number of values:", nx, "\n")
 
 def read():