why does the code snippet 1 behave differently than snippet 2?

Question

I have provided the entire code for context:

#include <bits/stdc++.h> 
using namespace std; 

const int MAX_CHARS = 256; 

// Function to find smallest window containing 
// all distinct characters 
string findSubString(string str) 
{ 
    int n = str.length(); 

    // Count all distinct characters. 
    int dist_count = 0; 
    bool visited[MAX_CHARS] = { false }; 
    for (int i = 0; i < n; i++) { 
        if (visited[str[i]] == false) { 
            visited[str[i]] = true; 
            dist_count++; 
        } 
    } 


    int start = 0, start_index = -1, min_len = INT_MAX; 

    int count = 0; 
    int curr_count[MAX_CHARS] = { 0 }; 
    for (int j = 0; j < n; j++) { 
        // Count occurrence of characters of string 
        curr_count[str[j]]++; 

        // If any distinct character matched, 
        // then increment count 
        if (curr_count[str[j]] == 1) 
            count++; 

        // if all the characters are matched 
        if (count == dist_count) { 

            // the section where i got it wrong
            while (curr_count[str[start]] > 1) {      
                if (curr_count[str[start]] > 1) 
                    curr_count[str[start]]--; 
                start++;
            } 
          // end section where i got it wrong

            // Update window size 
            int len_window = j - start + 1; 
            if (min_len > len_window) { 
                min_len = len_window; 
                start_index = start; 
            } 
        } 
    } 

    // Return substring starting from start_index 
    // and length min_len 
    return str.substr(start_index, min_len); 
} 

// Driver code 
int main() 
{ 
    string str = "aabcbcdbca"; 
    cout << "Smallest window containing all distinct"
            " characters is: "
        << findSubString(str); 
    return 0; 
} 

please correct me if i'm wrong. The while loop already checks for the condition where count(current_char)>1. If that's the case what is the need to check for IF?

        //code snippet 1:
        while (curr_count[str[start]] > 1) { 
                        if (curr_count[str[start]] > 1) 
                            curr_count[str[start]]--; 
                        start++; 
                    } 


        // code snippet 2:
        while (curr_count[str[start]] > 1) { 

                        curr_count[str[start]]--; 
                        start++; 
                    }

input: aabcbcdbca
output(considering snippet 1) : 4
output(considering snippet 2) : 6 // the start pointer wasn't incrementing