Fix -Wsign-conversion on GCC 8 (fixes #1715)

extras/tests/JsonObject/containsKey.cpp

@@ -29,7 +29,7 @@ TEST_CASE("JsonObject::containsKey()") {
 
 #ifdef HAS_VARIABLE_LENGTH_ARRAY
   SECTION("key is a VLA") {
-    int i = 16;
+    size_t i = 16;
     char vla[i];
     strcpy(vla, "hello");
 

extras/tests/JsonObject/createNestedArray.cpp

@@ -16,7 +16,7 @@ TEST_CASE("JsonObject::createNestedArray()") {
 
 #ifdef HAS_VARIABLE_LENGTH_ARRAY
   SECTION("key is a VLA") {
-    int i = 16;
+    size_t i = 16;
     char vla[i];
     strcpy(vla, "hello");
 

extras/tests/JsonObject/createNestedObject.cpp

@@ -15,7 +15,7 @@ TEST_CASE("JsonObject::createNestedObject()") {
 
 #ifdef HAS_VARIABLE_LENGTH_ARRAY
   SECTION("key is a VLA") {
-    int i = 16;
+    size_t i = 16;
     char vla[i];
     strcpy(vla, "hello");
 

extras/tests/JsonObject/remove.cpp

@@ -60,7 +60,7 @@ TEST_CASE("JsonObject::remove()") {
 
 #ifdef HAS_VARIABLE_LENGTH_ARRAY
   SECTION("key is a vla") {
-    int i = 16;
+    size_t i = 16;
     char vla[i];
     strcpy(vla, "b");
     obj.remove(vla);

extras/tests/JsonObject/subscript.cpp

@@ -172,7 +172,7 @@ TEST_CASE("JsonObject::operator[]") {
 #if defined(HAS_VARIABLE_LENGTH_ARRAY) && \
     !defined(SUBSCRIPT_CONFLICTS_WITH_BUILTIN_OPERATOR)
   SECTION("obj[VLA] = str") {
-    int i = 16;
+    size_t i = 16;
     char vla[i];
     strcpy(vla, "hello");
 
@@ -182,7 +182,7 @@ TEST_CASE("JsonObject::operator[]") {
   }
 
   SECTION("obj[str] = VLA") {  // issue #416
-    int i = 32;
+    size_t i = 32;
     char vla[i];
     strcpy(vla, "world");
 
@@ -192,7 +192,7 @@ TEST_CASE("JsonObject::operator[]") {
   }
 
   SECTION("obj.set(VLA, str)") {
-    int i = 16;
+    size_t i = 16;
     char vla[i];
     strcpy(vla, "hello");
 
@@ -202,7 +202,7 @@ TEST_CASE("JsonObject::operator[]") {
   }
 
   SECTION("obj.set(str, VLA)") {
-    int i = 32;
+    size_t i = 32;
     char vla[i];
     strcpy(vla, "world");
 
@@ -212,7 +212,7 @@ TEST_CASE("JsonObject::operator[]") {
   }
 
   SECTION("obj[VLA]") {
-    int i = 16;
+    size_t i = 16;
     char vla[i];
     strcpy(vla, "hello");