[BUGFIX] Many issues "If memory allocation fails, then there is a possible null pointer dereference:" fixed.

Author: Gonzalo Diaz

src/lib/exercises/src/hackerrank/warmup/mini_max_sum.c

@@ -37,6 +37,10 @@ char *HACKERRANK_WARMUP_miniMaxSumCalculate(int arr_count, const int *arr) {
 
 void HACKERRANK_WARMUP_miniMaxSum(int arr_count, const int *arr) {
   char *result = HACKERRANK_WARMUP_miniMaxSumCalculate(arr_count, arr);
+  if (result == NULL) {
+    return;
+  }
+
   printf("%s\n", result);
   free(result);
 }

src/lib/exercises/src/hackerrank/warmup/plus_minus.c

@@ -73,6 +73,9 @@ void HACKERRANK_WARMUP_freePlusMinus(char **plusMinusAnswer, int n) {
 
 void HACKERRANK_WARMUP_plusMinus(int arr_count, const int *arr) {
   char **output = HACKERRANK_WARMUP_plusMinusCalculate(arr_count, arr);
+  if (output == NULL) {
+    return;
+  }
 
   for (int i = 0; i < HACKERRANK_WARMUP_PLUSMINUS_LIMIT_ANSWERS; i++) {
     printf("%s", output[i]);

src/lib/exercises/src/hackerrank/warmup/staircase.c

@@ -45,6 +45,9 @@ void HACKERRANK_WARMUP_freeStaircase(char **staircase, int n) {
 
 void HACKERRANK_WARMUP_staircase(int n) {
   char **output = HACKERRANK_WARMUP_staircaseCalculate(n);
+  if (output == NULL) {
+    return;
+  }
 
   for (int i = 0; i < n; i++) {
     printf("%s\n", output[i]);

src/lib/exercises/src/hackerrank/warmup/time_conversion.c

@@ -54,6 +54,10 @@ char *HACKERRANK_WARMUP_timeConversion(const char *s) {
   char *conversion =
       malloc((HACKERRANK_WARMUP_SHORT_TIME_FORMAT_SIZE + 1) * sizeof(char));
 
+  if (conversion == NULL) {
+    return NULL;
+  }
+
   for (int i = 0; i < HACKERRANK_WARMUP_SHORT_TIME_FORMAT_SIZE; i++) {
     conversion[i] = s[i];
   }